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Assignment operators assign values to JavaScript variables.
Operator | Example | Same As |
---|---|---|
= | x = y | x = y |
+= | x += y | x = x + y |
-= | x -= y | x = x - y |
*= | x *= y | x = x * y |
/= | x /= y | x = x / y |
%= | x %= y | x = x % y |
**= | x **= y | x = x ** y |
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Shift Assignment Operators
Operator | Example | Same As |
---|---|---|
<<= | x <<= y | x = x << y |
>>= | x >>= y | x = x >> y |
>>>= | x >>>= y | x = x >>> y |
Bitwise Assignment Operators
Operator | Example | Same As |
---|---|---|
&= | x &= y | x = x & y |
^= | x ^= y | x = x ^ y |
|= | x |= y | x = x | y |
Logical Assignment Operators
Operator | Example | Same As |
---|---|---|
&&= | x &&= y | x = x && (x = y) |
||= | x ||= y | x = x || (x = y) |
??= | x ??= y | x = x ?? (x = y) |
The = Operator
The Simple Assignment Operator assigns a value to a variable.
Simple Assignment Examples
The += operator.
The Addition Assignment Operator adds a value to a variable.
Addition Assignment Examples
The -= operator.
The Subtraction Assignment Operator subtracts a value from a variable.
Subtraction Assignment Example
The *= operator.
The Multiplication Assignment Operator multiplies a variable.
Multiplication Assignment Example
The **= operator.
The Exponentiation Assignment Operator raises a variable to the power of the operand.
Exponentiation Assignment Example
The /= operator.
The Division Assignment Operator divides a variable.
Division Assignment Example
The %= operator.
The Remainder Assignment Operator assigns a remainder to a variable.
Remainder Assignment Example
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The <<= Operator
The Left Shift Assignment Operator left shifts a variable.
Left Shift Assignment Example
The >>= operator.
The Right Shift Assignment Operator right shifts a variable (signed).
Right Shift Assignment Example
The >>>= operator.
The Unsigned Right Shift Assignment Operator right shifts a variable (unsigned).
Unsigned Right Shift Assignment Example
The &= operator.
The Bitwise AND Assignment Operator does a bitwise AND operation on two operands and assigns the result to the the variable.
Bitwise AND Assignment Example
The |= operator.
The Bitwise OR Assignment Operator does a bitwise OR operation on two operands and assigns the result to the variable.
Bitwise OR Assignment Example
The ^= operator.
The Bitwise XOR Assignment Operator does a bitwise XOR operation on two operands and assigns the result to the variable.
Bitwise XOR Assignment Example
The &&= operator.
The Logical AND assignment operator is used between two values.
If the first value is true, the second value is assigned.
Logical AND Assignment Example
The &&= operator is an ES2020 feature .
The ||= Operator
The Logical OR assignment operator is used between two values.
If the first value is false, the second value is assigned.
Logical OR Assignment Example
The ||= operator is an ES2020 feature .
The ??= Operator
The Nullish coalescing assignment operator is used between two values.
If the first value is undefined or null, the second value is assigned.
Nullish Coalescing Assignment Example
The ??= operator is an ES2020 feature .
Test Yourself With Exercises
Use the correct assignment operator that will result in x being 15 (same as x = x + y ).
Start the Exercise
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Home » JavaScript Tutorial » JavaScript Assignment Operators
JavaScript Assignment Operators
Summary : in this tutorial, you will learn how to use JavaScript assignment operators to assign a value to a variable.
Introduction to JavaScript assignment operators
An assignment operator ( = ) assigns a value to a variable. The syntax of the assignment operator is as follows:
In this syntax, JavaScript evaluates the expression b first and assigns the result to the variable a .
The following example declares the counter variable and initializes its value to zero:
The following example increases the counter variable by one and assigns the result to the counter variable:
When evaluating the second statement, JavaScript evaluates the expression on the right-hand first ( counter + 1 ) and assigns the result to the counter variable. After the second assignment, the counter variable is 1 .
To make the code more concise, you can use the += operator like this:
In this syntax, you don’t have to repeat the counter variable twice in the assignment.
The following table illustrates assignment operators that are shorthand for another operator and the assignment:
Operator | Meaning | Description |
---|---|---|
Assigns the value of to . | ||
Assigns the result of plus to . | ||
Assigns the result of minus to . | ||
Assigns the result of times to . | ||
Assigns the result of divided by to . | ||
Assigns the result of modulo to . | ||
Assigns the result of AND to . | ||
Assigns the result of OR to . | ||
Assigns the result of XOR to . | ||
Assigns the result of shifted left by to . | ||
Assigns the result of shifted right (sign preserved) by to . | ||
Assigns the result of shifted right by to . |
Chaining JavaScript assignment operators
If you want to assign a single value to multiple variables, you can chain the assignment operators. For example:
In this example, JavaScript evaluates from right to left. Therefore, it does the following:
- Use the assignment operator ( = ) to assign a value to a variable.
- Chain the assignment operators if you want to assign a single value to multiple variables.
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JAVASCRIPT ASSIGNMENT OPERATORS
In this tutorial, you will learn about all the different assignment operators in javascript and how to use them in javascript.
Assignment Operators
In javascript, there are 16 different assignment operators that are used to assign value to the variable. It is shorthand of other operators which is recommended to use.
The assignment operators are used to assign value based on the right operand to its left operand.
The left operand must be a variable while the right operand may be a variable, number, boolean, string, expression, object, or combination of any other.
One of the most basic assignment operators is equal = , which is used to directly assign a value.
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Assignment Operators List
Here is the list of all assignment operators in JavaScript:
In the following table if variable a is not defined then assume it to be 10.
Operator | Description | Example | Equivalent to |
---|---|---|---|
= | a = 10 | a = 10 | |
+= | a += 10 | a = a + 10 | |
-= | a -= 10 | a = a - 10 | |
*= | a *= 10 | a = a * 10 | |
/= | a /= 10 | a = a / 10 | |
%= | a %= 10 | a = a % 10 | |
**= | a **= 2 | a = a ** 2 | |
<<= | a <<= 1 | a = a << 1 | |
>>= | a >>= 2 | a = a >> 2 | |
>>>= | a >>>= 1 | a = a >>> 1 | |
&= | a &= 4 | a = a & 4 | |
|= | a |= 2 | a = a | 2 | |
^= | a ^= 5 | a = a ^ 5 | |
&&= | a &&= 3 | a = a && 3 | |
||= | a ||= 4 | a = a || 4 | |
??= | a ??= 2 | a = a ?? 2 |
Assignment operator
The assignment operator = is the simplest value assigning operator which assigns a given value to a variable.
The assignment operators support chaining, which means you can assign a single value in multiple variables in a single line.
Addition assignment operator
The addition assignment operator += is used to add the value of the right operand to the value of the left operand and assigns the result to the left operand.
On the basis of the data type of variable, the addition assignment operator may add or concatenate the variables.
Subtraction assignment operator
The subtraction assignment operator -= subtracts the value of the right operand from the value of the left operand and assigns the result to the left operand.
If the value can not be subtracted then it results in a NaN .
Multiplication assignment operator
The multiplication assignment operator *= assigns the result to the left operand after multiplying values of the left and right operand.
Division assignment operator
The division assignment operator /= divides the value of the left operand by the value of the right operand and assigns the result to the left operand.
Remainder assignment operator
The remainder assignment operator %= assigns the remainder to the left operand after dividing the value of the left operand by the value of the right operand.
Exponentiation assignment operator
The exponential assignment operator **= assigns the result of exponentiation to the left operand after exponentiating the value of the left operand by the value of the right operand.
Left shift assignment
The left shift assignment operator <<= assigns the result of the left shift to the left operand after shifting the value of the left operand by the value of the right operand.
Right shift assignment
The right shift assignment operator >>= assigns the result of the right shift to the left operand after shifting the value of the left operand by the value of the right operand.
Unsigned right shift assignment
The unsigned right shift assignment operator >>>= assigns the result of the unsigned right shift to the left operand after shifting the value of the left operand by the value of the right operand.
Bitwise AND assignment
The bitwise AND assignment operator &= assigns the result of bitwise AND to the left operand after ANDing the value of the left operand by the value of the right operand.
Bitwise OR assignment
The bitwise OR assignment operator |= assigns the result of bitwise OR to the left operand after ORing the value of left operand by the value of the right operand.
Bitwise XOR assignment
The bitwise XOR assignment operator ^= assigns the result of bitwise XOR to the left operand after XORing the value of the left operand by the value of the right operand.
Logical AND assignment
The logical AND assignment operator &&= assigns value to left operand only when it is truthy .
Note : A truthy value is a value that is considered true when encountered in a boolean context.
Logical OR assignment
The logical OR assignment operator ||= assigns value to left operand only when it is falsy .
Note : A falsy value is a value that is considered false when encountered in a boolean context.
Logical nullish assignment
The logical nullish assignment operator ??= assigns value to left operand only when it is nullish ( null or undefined ).
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Left-hand-side expressions
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This chapter describes JavaScript's expressions and operators, including assignment, comparison, arithmetic, bitwise, logical, string, ternary and more.
A complete and detailed list of operators and expressions is also available in the reference .
JavaScript has the following types of operators. This section describes the operators and contains information about operator precedence.
- Assignment operators
- Comparison operators
- Arithmetic operators
- Bitwise operators
Logical operators
String operators, conditional (ternary) operator.
- Comma operator
Unary operators
- Relational operator
JavaScript has both binary and unary operators, and one special ternary operator, the conditional operator. A binary operator requires two operands, one before the operator and one after the operator:
For example, 3+4 or x*y .
A unary operator requires a single operand, either before or after the operator:
For example, x++ or ++x .
An assignment operator assigns a value to its left operand based on the value of its right operand. The simple assignment operator is equal ( = ), which assigns the value of its right operand to its left operand. That is, x = y assigns the value of y to x .
There are also compound assignment operators that are shorthand for the operations listed in the following table:
Name | Shorthand operator | Meaning |
---|---|---|
Destructuring
For more complex assignments, the destructuring assignment syntax is a JavaScript expression that makes it possible to extract data from arrays or objects using a syntax that mirrors the construction of array and object literals.
A comparison operator compares its operands and returns a logical value based on whether the comparison is true. The operands can be numerical, string, logical, or object values. Strings are compared based on standard lexicographical ordering, using Unicode values. In most cases, if the two operands are not of the same type, JavaScript attempts to convert them to an appropriate type for the comparison. This behavior generally results in comparing the operands numerically. The sole exceptions to type conversion within comparisons involve the === and !== operators, which perform strict equality and inequality comparisons. These operators do not attempt to convert the operands to compatible types before checking equality. The following table describes the comparison operators in terms of this sample code:
Operator | Description | Examples returning true |
---|---|---|
( ) | Returns if the operands are equal. |
|
( ) | Returns if the operands are not equal. | |
( ) | Returns if the operands are equal and of the same type. See also and . | |
( ) | Returns if the operands are of the same type but not equal, or are of different type. | |
( ) | Returns if the left operand is greater than the right operand. | |
( ) | Returns if the left operand is greater than or equal to the right operand. | |
( ) | Returns if the left operand is less than the right operand. | |
( ) | Returns if the left operand is less than or equal to the right operand. |
Note: ( => ) is not an operator, but the notation for Arrow functions .
An arithmetic operator takes numerical values (either literals or variables) as their operands and returns a single numerical value. The standard arithmetic operators are addition ( + ), subtraction ( - ), multiplication ( * ), and division ( / ). These operators work as they do in most other programming languages when used with floating point numbers (in particular, note that division by zero produces Infinity ). For example:
In addition to the standard arithmetic operations (+, -, * /), JavaScript provides the arithmetic operators listed in the following table:
Operator | Description | Example |
---|---|---|
( ) | Binary operator. Returns the integer remainder of dividing the two operands. | 12 % 5 returns 2. |
( ) | Unary operator. Adds one to its operand. If used as a prefix operator ( ), returns the value of its operand after adding one; if used as a postfix operator ( ), returns the value of its operand before adding one. | If is 3, then sets to 4 and returns 4, whereas returns 3 and, only then, sets to 4. |
( ) | Unary operator. Subtracts one from its operand. The return value is analogous to that for the increment operator. | If is 3, then sets to 2 and returns 2, whereas returns 3 and, only then, sets to 2. |
( ) | Unary operator. Returns the negation of its operand. | If is 3, then returns -3. |
( ) | Unary operator. Attempts to convert the operand to a number, if it is not already. | returns . returns |
( ) | Calculates the to the power, that is, | returns . returns . |
A bitwise operator treats their operands as a set of 32 bits (zeros and ones), rather than as decimal, hexadecimal, or octal numbers. For example, the decimal number nine has a binary representation of 1001. Bitwise operators perform their operations on such binary representations, but they return standard JavaScript numerical values.
The following table summarizes JavaScript's bitwise operators.
Operator | Usage | Description |
---|---|---|
Returns a one in each bit position for which the corresponding bits of both operands are ones. | ||
Returns a zero in each bit position for which the corresponding bits of both operands are zeros. | ||
Returns a zero in each bit position for which the corresponding bits are the same. [Returns a one in each bit position for which the corresponding bits are different.] | ||
Inverts the bits of its operand. | ||
Shifts in binary representation bits to the left, shifting in zeros from the right. | ||
Shifts in binary representation bits to the right, discarding bits shifted off. | ||
Shifts in binary representation bits to the right, discarding bits shifted off, and shifting in zeros from the left. |
Bitwise logical operators
Conceptually, the bitwise logical operators work as follows:
- The operands are converted to thirty-two-bit integers and expressed by a series of bits (zeros and ones). Numbers with more than 32 bits get their most significant bits discarded. For example, the following integer with more than 32 bits will be converted to a 32 bit integer: Before: 11100110111110100000000000000110000000000001 After: 10100000000000000110000000000001
- Each bit in the first operand is paired with the corresponding bit in the second operand: first bit to first bit, second bit to second bit, and so on.
- The operator is applied to each pair of bits, and the result is constructed bitwise.
For example, the binary representation of nine is 1001, and the binary representation of fifteen is 1111. So, when the bitwise operators are applied to these values, the results are as follows:
Expression | Result | Binary Description |
---|---|---|
Note that all 32 bits are inverted using the Bitwise NOT operator, and that values with the most significant (left-most) bit set to 1 represent negative numbers (two's-complement representation).
Bitwise shift operators
The bitwise shift operators take two operands: the first is a quantity to be shifted, and the second specifies the number of bit positions by which the first operand is to be shifted. The direction of the shift operation is controlled by the operator used.
Shift operators convert their operands to thirty-two-bit integers and return a result of the same type as the left operand.
The shift operators are listed in the following table.
Operator | Description | Example |
---|---|---|
( ) | This operator shifts the first operand the specified number of bits to the left. Excess bits shifted off to the left are discarded. Zero bits are shifted in from the right. | yields 36, because 1001 shifted 2 bits to the left becomes 100100, which is 36. |
( ) | This operator shifts the first operand the specified number of bits to the right. Excess bits shifted off to the right are discarded. Copies of the leftmost bit are shifted in from the left. | yields 2, because 1001 shifted 2 bits to the right becomes 10, which is 2. Likewise, yields -3, because the sign is preserved. |
( ) | This operator shifts the first operand the specified number of bits to the right. Excess bits shifted off to the right are discarded. Zero bits are shifted in from the left. | yields 4, because 10011 shifted 2 bits to the right becomes 100, which is 4. For non-negative numbers, zero-fill right shift and sign-propagating right shift yield the same result. |
Logical operators are typically used with Boolean (logical) values; when they are, they return a Boolean value. However, the && and || operators actually return the value of one of the specified operands, so if these operators are used with non-Boolean values, they may return a non-Boolean value. The logical operators are described in the following table.
Operator | Usage | Description |
---|---|---|
( ) | Returns if it can be converted to ; otherwise, returns . Thus, when used with Boolean values, returns if both operands are true; otherwise, returns . | |
( ) | Returns if it can be converted to ; otherwise, returns . Thus, when used with Boolean values, returns if either operand is true; if both are false, returns . | |
( ) | Returns if its single operand can be converted to ; otherwise, returns . |
Examples of expressions that can be converted to false are those that evaluate to null, 0, NaN, the empty string (""), or undefined.
The following code shows examples of the && (logical AND) operator.
The following code shows examples of the || (logical OR) operator.
The following code shows examples of the ! (logical NOT) operator.
Short-circuit evaluation
As logical expressions are evaluated left to right, they are tested for possible "short-circuit" evaluation using the following rules:
- false && anything is short-circuit evaluated to false.
- true || anything is short-circuit evaluated to true.
The rules of logic guarantee that these evaluations are always correct. Note that the anything part of the above expressions is not evaluated, so any side effects of doing so do not take effect.
In addition to the comparison operators, which can be used on string values, the concatenation operator (+) concatenates two string values together, returning another string that is the union of the two operand strings.
For example,
The shorthand assignment operator += can also be used to concatenate strings.
The conditional operator is the only JavaScript operator that takes three operands. The operator can have one of two values based on a condition. The syntax is:
If condition is true, the operator has the value of val1 . Otherwise it has the value of val2 . You can use the conditional operator anywhere you would use a standard operator.
This statement assigns the value "adult" to the variable status if age is eighteen or more. Otherwise, it assigns the value "minor" to status .
The comma operator ( , ) simply evaluates both of its operands and returns the value of the last operand. This operator is primarily used inside a for loop, to allow multiple variables to be updated each time through the loop.
For example, if a is a 2-dimensional array with 10 elements on a side, the following code uses the comma operator to update two variables at once. The code prints the values of the diagonal elements in the array:
A unary operation is an operation with only one operand.
The delete operator deletes an object, an object's property, or an element at a specified index in an array. The syntax is:
where objectName is the name of an object, property is an existing property, and index is an integer representing the location of an element in an array.
The fourth form is legal only within a with statement, to delete a property from an object.
You can use the delete operator to delete variables declared implicitly but not those declared with the var statement.
If the delete operator succeeds, it sets the property or element to undefined . The delete operator returns true if the operation is possible; it returns false if the operation is not possible.
Deleting array elements
When you delete an array element, the array length is not affected. For example, if you delete a[3] , a[4] is still a[4] and a[3] is undefined.
When the delete operator removes an array element, that element is no longer in the array. In the following example, trees[3] is removed with delete . However, trees[3] is still addressable and returns undefined .
If you want an array element to exist but have an undefined value, use the undefined keyword instead of the delete operator. In the following example, trees[3] is assigned the value undefined , but the array element still exists:
The typeof operator is used in either of the following ways:
The typeof operator returns a string indicating the type of the unevaluated operand. operand is the string, variable, keyword, or object for which the type is to be returned. The parentheses are optional.
Suppose you define the following variables:
The typeof operator returns the following results for these variables:
For the keywords true and null , the typeof operator returns the following results:
For a number or string, the typeof operator returns the following results:
For property values, the typeof operator returns the type of value the property contains:
For methods and functions, the typeof operator returns results as follows:
For predefined objects, the typeof operator returns results as follows:
The void operator is used in either of the following ways:
The void operator specifies an expression to be evaluated without returning a value. expression is a JavaScript expression to evaluate. The parentheses surrounding the expression are optional, but it is good style to use them.
You can use the void operator to specify an expression as a hypertext link. The expression is evaluated but is not loaded in place of the current document.
The following code creates a hypertext link that does nothing when the user clicks it. When the user clicks the link, void(0) evaluates to undefined , which has no effect in JavaScript.
The following code creates a hypertext link that submits a form when the user clicks it.
Relational operators
A relational operator compares its operands and returns a Boolean value based on whether the comparison is true.
The in operator returns true if the specified property is in the specified object. The syntax is:
where propNameOrNumber is a string or numeric expression representing a property name or array index, and objectName is the name of an object.
The following examples show some uses of the in operator.
The instanceof operator returns true if the specified object is of the specified object type. The syntax is:
where objectName is the name of the object to compare to objectType , and objectType is an object type, such as Date or Array .
Use instanceof when you need to confirm the type of an object at runtime. For example, when catching exceptions, you can branch to different exception-handling code depending on the type of exception thrown.
For example, the following code uses instanceof to determine whether theDay is a Date object. Because theDay is a Date object, the statements in the if statement execute.
The precedence of operators determines the order they are applied when evaluating an expression. You can override operator precedence by using parentheses.
The following table describes the precedence of operators, from highest to lowest.
Operator type | Individual operators |
---|---|
member | |
call / create instance | |
negation/increment | |
multiply/divide | |
addition/subtraction | |
bitwise shift | |
relational | |
equality | |
bitwise-and | |
bitwise-xor | |
bitwise-or | |
logical-and | |
logical-or | |
conditional | |
assignment | |
comma |
A more detailed version of this table, complete with links to additional details about each operator, may be found in JavaScript Reference .
- Expressions
An expression is any valid unit of code that resolves to a value.
Every syntactically valid expression resolves to some value but conceptually, there are two types of expressions: with side effects (for example: those that assign value to a variable) and those that in some sense evaluates and therefore resolves to value.
The expression x = 7 is an example of the first type. This expression uses the = operator to assign the value seven to the variable x . The expression itself evaluates to seven.
The code 3 + 4 is an example of the second expression type. This expression uses the + operator to add three and four together without assigning the result, seven, to a variable. JavaScript has the following expression categories:
- Arithmetic: evaluates to a number, for example 3.14159. (Generally uses arithmetic operators .)
- String: evaluates to a character string, for example, "Fred" or "234". (Generally uses string operators .)
- Logical: evaluates to true or false. (Often involves logical operators .)
- Primary expressions: Basic keywords and general expressions in JavaScript.
- Left-hand-side expressions: Left values are the destination of an assignment.
Primary expressions
Basic keywords and general expressions in JavaScript.
Use the this keyword to refer to the current object. In general, this refers to the calling object in a method. Use this either with the dot or the bracket notation:
Suppose a function called validate validates an object's value property, given the object and the high and low values:
You could call validate in each form element's onChange event handler, using this to pass it the form element, as in the following example:
- Grouping operator
The grouping operator ( ) controls the precedence of evaluation in expressions. For example, you can override multiplication and division first, then addition and subtraction to evaluate addition first.
Comprehensions
Comprehensions are an experimental JavaScript feature, targeted to be included in a future ECMAScript version. There are two versions of comprehensions:
Comprehensions exist in many programming languages and allow you to quickly assemble a new array based on an existing one, for example.
Left values are the destination of an assignment.
You can use the new operator to create an instance of a user-defined object type or of one of the built-in object types. Use new as follows:
The super keyword is used to call functions on an object's parent. It is useful with classes to call the parent constructor, for example.
Spread operator
The spread operator allows an expression to be expanded in places where multiple arguments (for function calls) or multiple elements (for array literals) are expected.
Example: Today if you have an array and want to create a new array with the existing one being part of it, the array literal syntax is no longer sufficient and you have to fall back to imperative code, using a combination of push , splice , concat , etc. With spread syntax this becomes much more succinct:
Similarly, the spread operator works with function calls:
Document Tags and Contributors
- l10n:priority
- JavaScript basics
- JavaScript first steps
- JavaScript building blocks
- Introducing JavaScript objects
- Introduction
- Grammar and types
- Control flow and error handling
- Loops and iteration
- Numbers and dates
- Text formatting
- Regular expressions
- Indexed collections
- Keyed collections
- Working with objects
- Details of the object model
- Iterators and generators
- Meta programming
- A re-introduction to JavaScript
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- Equality comparisons and sameness
- Inheritance and the prototype chain
- Strict mode
- JavaScript typed arrays
- Memory Management
- Concurrency model and Event Loop
- References:
- ArrayBuffer
- AsyncFunction
- Float32Array
- Float64Array
- GeneratorFunction
- InternalError
- Intl.Collator
- Intl.DateTimeFormat
- Intl.NumberFormat
- ParallelArray
- ReferenceError
- SIMD.Bool16x8
- SIMD.Bool32x4
- SIMD.Bool64x2
- SIMD.Bool8x16
- SIMD.Float32x4
- SIMD.Float64x2
- SIMD.Int16x8
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- SIMD.Int8x16
- SIMD.Uint16x8
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- SIMD.Uint8x16
- SharedArrayBuffer
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- Uint16Array
- Uint32Array
- Uint8ClampedArray
- WebAssembly
- decodeURI()
- decodeURIComponent()
- encodeURI()
- encodeURIComponent()
- parseFloat()
- Array comprehensions
- Conditional (ternary) Operator
- Destructuring assignment
- Expression closures
- Generator comprehensions
- Legacy generator function expression
- Logical Operators
- Object initializer
- Property accessors
- Spread syntax
- async function expression
- class expression
- delete operator
- function expression
- function* expression
- in operator
- new operator
- void operator
- Legacy generator function
- async function
- for each...in
- function declaration
- try...catch
- Arguments object
- Arrow functions
- Default parameters
- Method definitions
- Rest parameters
- constructor
- element loaded from a different domain for which you violated the same-origin policy.">Error: Permission denied to access property "x"
- InternalError: too much recursion
- RangeError: argument is not a valid code point
- RangeError: invalid array length
- RangeError: invalid date
- RangeError: precision is out of range
- RangeError: radix must be an integer
- RangeError: repeat count must be less than infinity
- RangeError: repeat count must be non-negative
- ReferenceError: "x" is not defined
- ReferenceError: assignment to undeclared variable "x"
- ReferenceError: can't access lexical declaration`X' before initialization
- ReferenceError: deprecated caller or arguments usage
- ReferenceError: invalid assignment left-hand side
- ReferenceError: reference to undefined property "x"
- SyntaxError: "0"-prefixed octal literals and octal escape seq. are deprecated
- SyntaxError: "use strict" not allowed in function with non-simple parameters
- SyntaxError: "x" is a reserved identifier
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- Assignment operators
An assignment operator assigns a value to its left operand based on the value of its right operand.
The basic assignment operator is equal ( = ), which assigns the value of its right operand to its left operand. That is, x = y assigns the value of y to x . The other assignment operators are usually shorthand for standard operations, as shown in the following definitions and examples.
Name | Shorthand operator | Meaning |
---|---|---|
Simple assignment operator which assigns a value to a variable. Chaining the assignment operator is possible in order to assign a single value to multiple variables. See the example.
Addition assignment
The addition assignment operator adds the value of the right operand to a variable and assigns the result to the variable. The types of the two operands determine the behavior of the addition assignment operator. Addition or concatenation is possible. See the addition operator for more details.
Subtraction assignment
The subtraction assignment operator subtracts the value of the right operand from a variable and assigns the result to the variable. See the subtraction operator for more details.
Multiplication assignment
The multiplication assignment operator multiplies a variable by the value of the right operand and assigns the result to the variable. See the multiplication operator for more details.
Division assignment
The division assignment operator divides a variable by the value of the right operand and assigns the result to the variable. See the division operator for more details.
Remainder assignment
The remainder assignment operator divides a variable by the value of the right operand and assigns the remainder to the variable. See the remainder operator for more details.
Left shift assignment
The left shift assignment operator moves the specified amount of bits to the left and assigns the result to the variable. See the left shift operator for more details.
Right shift assignment
The right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the right shift operator for more details.
Unsigned right shift assignment
The unsigned right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the unsigned right shift operator for more details.
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Bitwise AND assignment
The bitwise AND assignment operator uses the binary representation of both operands, does a bitwise AND operation on them and assigns the result to the variable. See the bitwise AND operator for more details.
Bitwise XOR assignment
The bitwise XOR assignment operator uses the binary representation of both operands, does a bitwise XOR operation on them and assigns the result to the variable. See the bitwise XOR operator for more details.
Bitwise OR assignment
The bitwise OR assignment operator uses the binary representation of both operands, does a bitwise OR operation on them and assigns the result to the variable. See the bitwise OR operator for more details.
Left operand with another assignment operator
In unusual situations, the assignment operator (e.g. x += y ) is not identical to the meaning expression (here x = x + y ). When the left operand of an assignment operator itself contains an assignment operator, the left operand is evaluated only once. For example:
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 1st Edition. | Standard | Initial definition. |
Standard | ||
Release Candidate |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
- Arithmetic operators
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JavaScript operators are special symbols that perform operations on one or more operands (values). For example,
Here, we used the + operator to add the operands 2 and 3 .
JavaScript Operator Types
Here is a list of different JavaScript operators you will learn in this tutorial:
- Arithmetic Operators
- Assignment Operators
- Comparison Operators
- Logical Operators
- Bitwise Operators
- String Operators
- Miscellaneous Operators
1. JavaScript Arithmetic Operators
We use arithmetic operators to perform arithmetic calculations like addition, subtraction, etc. For example,
Here, we used the - operator to subtract 3 from 5 .
Commonly Used Arithmetic Operators
Operator | Name | Example |
---|---|---|
Addition | ||
Subtraction | ||
Multiplication | ||
Division | ||
Remainder | ||
Increment (increments by ) | or | |
Decrement (decrements by ) | or | |
Exponentiation (Power) |
Example 1: Arithmetic Operators in JavaScript
Note: The increment operator ++ adds 1 to the operand. And, the decrement operator -- decreases the value of the operand by 1 .
To learn more, visit Increment ++ and Decrement -- Operators .
2. JavaScript Assignment Operators
We use assignment operators to assign values to variables. For example,
Here, we used the = operator to assign the value 5 to the variable x .
Commonly Used Assignment Operators
Operator | Name | Example |
---|---|---|
Assignment Operator | ||
Addition Assignment | ||
Subtraction Assignment | ||
Multiplication Assignment | ||
Division Assignment | ||
Remainder Assignment | ||
Exponentiation Assignment |
Example 2: Assignment Operators in JavaScript
3. javascript comparison operators.
We use comparison operators to compare two values and return a boolean value ( true or false ). For example,
Here, we have used the > comparison operator to check whether a (whose value is 3 ) is greater than b (whose value is 2 ).
Since 3 is greater than 2 , we get true as output.
Note: In the above example, a > b is called a boolean expression since evaluating it results in a boolean value.
Commonly Used Comparison Operators
Operator | Meaning | Example |
---|---|---|
Equal to | gives us | |
Not equal to | gives us | |
Greater than | gives us | |
Less than | gives us | |
Greater than or equal to | gives us | |
Less than or equal to | gives us | |
Strictly equal to | gives us | |
Strictly not equal to | gives us |
Example 3: Comparison Operators in JavaScript
The equality operators ( == and != ) convert both operands to the same type before comparing their values. For example,
Here, we used the == operator to compare the number 3 and the string 3 .
By default, JavaScript converts string 3 to number 3 and compares the values.
However, the strict equality operators ( === and !== ) do not convert operand types before comparing their values. For example,
Here, JavaScript didn't convert string 4 to number 4 before comparing their values.
Thus, the result is false , as number 4 isn't equal to string 4 .
4. JavaScript Logical Operators
We use logical operators to perform logical operations on boolean expressions. For example,
Here, && is the logical operator AND . Since both x < 6 and y < 5 are true , the combined result is true .
Commonly Used Logical Operators
Operator | Syntax | Description |
---|---|---|
(Logical AND) | only if both and are | |
(Logical OR) | if either or is | |
(Logical NOT) | if is and vice versa |
Example 4: Logical Operators in JavaScript
Note: We use comparison and logical operators in decision-making and loops. You will learn about them in detail in later tutorials.
More on JavaScript Operators
We use bitwise operators to perform binary operations on integers.
Operator | Description | Example |
---|---|---|
& | Bitwise AND | |
| | Bitwise OR | |
^ | Bitwise XOR | |
~ | Bitwise NOT | |
<< | Left shift | |
>> | Sign-propagating right shift | |
>>> | Zero-fill right shift |
Note: We rarely use bitwise operators in everyday programming. If you are interested, visit JavaScript Bitwise Operators to learn more.
In JavaScript, you can also use the + operator to concatenate (join) two strings. For example,
Here, we used the + operator to concatenate str1 and str2 .
JavaScript has many more operators besides the ones we listed above. You will learn about them in detail in later tutorials.
Operator | Description | Example |
---|---|---|
: Evaluates multiple operands and returns the value of the last operand. | ||
: Returns value based on the condition. | ||
Returns the data type of the variable. | ||
Returns t if the specified object is a valid object of the specified class. | ||
Discards any expression's return value. |
Table of Contents
- Introduction
- JavaScript Arithmetic Operators
- JavaScript Assignment Operators
- JavaScript Comparison Operators
- JavaScript Logical Operators
Video: JavaScript Operators
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An assignment operator assigns a value to its left operand based on the value of its right operand.
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The basic assignment operator is equal ( = ), which assigns the value of its right operand to its left operand. That is, x = y assigns the value of y to x . The other assignment operators are usually shorthand for standard operations, as shown in the following definitions and examples.
Name | Shorthand operator | Meaning |
---|---|---|
Simple assignment operator is used to assign a value to a variable. The assignment operation evaluates to the assigned value. Chaining the assignment operator is possible in order to assign a single value to multiple variables. See the example.
Addition assignment
The addition assignment operator adds the value of the right operand to a variable and assigns the result to the variable. The types of the two operands determine the behavior of the addition assignment operator. Addition or concatenation is possible. See the addition operator for more details.
Subtraction assignment
The subtraction assignment operator subtracts the value of the right operand from a variable and assigns the result to the variable. See the subtraction operator for more details.
Multiplication assignment
The multiplication assignment operator multiplies a variable by the value of the right operand and assigns the result to the variable. See the multiplication operator for more details.
Division assignment
The division assignment operator divides a variable by the value of the right operand and assigns the result to the variable. See the division operator for more details.
Remainder assignment
The remainder assignment operator divides a variable by the value of the right operand and assigns the remainder to the variable. See the remainder operator for more details.
Exponentiation assignment
The exponentiation assignment operator evaluates to the result of raising first operand to the power second operand. See the exponentiation operator for more details.
Left shift assignment
The left shift assignment operator moves the specified amount of bits to the left and assigns the result to the variable. See the left shift operator for more details.
Right shift assignment
The right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the right shift operator for more details.
Unsigned right shift assignment
The unsigned right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the unsigned right shift operator for more details.
Bitwise AND assignment
The bitwise AND assignment operator uses the binary representation of both operands, does a bitwise AND operation on them and assigns the result to the variable. See the bitwise AND operator for more details.
Bitwise XOR assignment
The bitwise XOR assignment operator uses the binary representation of both operands, does a bitwise XOR operation on them and assigns the result to the variable. See the bitwise XOR operator for more details.
Bitwise OR assignment
The bitwise OR assignment operator uses the binary representation of both operands, does a bitwise OR operation on them and assigns the result to the variable. See the bitwise OR operator for more details.
Left operand with another assignment operator
In unusual situations, the assignment operator (e.g. x += y ) is not identical to the meaning expression (here x = x + y ). When the left operand of an assignment operator itself contains an assignment operator, the left operand is evaluated only once. For example:
Specification | Status | Comment |
---|---|---|
Draft | ||
Standard | ||
Standard | ||
Standard | Initial definition. |
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | Android webview | Chrome for Android | Edge Mobile | Firefox for Android | Opera for Android | Safari on iOS | Samsung Internet | Node.js | |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
) | Chrome 52 | Edge | Firefox 52 | IE No | Opera Yes | Safari 10.1 | WebView Android 51 | Chrome Android 52 | Edge Mobile | Firefox Android 52 | Opera Android Yes | Safari iOS 10.1 | Samsung Internet Android 6.0 | nodejs 7.0.0 7.0.0 6.5.0 From version 6.5.0: this feature is behind the runtime flag. |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
) | Chrome Yes | Edge Yes | Firefox 1 | IE Yes | Opera Yes | Safari Yes | WebView Android Yes | Chrome Android Yes | Edge Mobile Yes | Firefox Android 4 | Opera Android Yes | Safari iOS Yes | Samsung Internet Android Yes | nodejs Yes |
- Arithmetic operators
Document Tags and Contributors
- JavaScript basics
- JavaScript first steps
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- Introducing JavaScript objects
- Introduction
- Grammar and types
- Control flow and error handling
- Loops and iteration
- Expressions and operators
- Numbers and dates
- Text formatting
- Regular expressions
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- Keyed collections
- Working with objects
- Details of the object model
- Using promises
- Iterators and generators
- Meta programming
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- A re-introduction to JavaScript
- JavaScript data structures
- Equality comparisons and sameness
- Inheritance and the prototype chain
- Strict mode
- JavaScript typed arrays
- Memory Management
- Concurrency model and Event Loop
- References:
- ArrayBuffer
- AsyncFunction
- Float32Array
- Float64Array
- GeneratorFunction
- InternalError
- Intl.Collator
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- WebAssembly
- decodeURI()
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- parseFloat()
- Array comprehensions
- Bitwise operators
- Comma operator
- Comparison operators
- Conditional (ternary) operator
- Destructuring assignment
- Expression closures
- Generator comprehensions
- Grouping operator
- Legacy generator function expression
- Logical operators
- Object initializer
- Operator precedence
- (currently at stage 1) pipes the value of an expression into a function. This allows the creation of chained function calls in a readable manner. The result is syntactic sugar in which a function call with a single argument can be written like this:">Pipeline operator
- Property accessors
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- element loaded from a different domain for which you violated the same-origin policy.">Error: Permission denied to access property "x"
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- SyntaxError: for-in loop head declarations may not have initializers
- SyntaxError: function statement requires a name
- SyntaxError: identifier starts immediately after numeric literal
- SyntaxError: illegal character
- SyntaxError: invalid regular expression flag "x"
- SyntaxError: missing ) after argument list
- SyntaxError: missing ) after condition
- SyntaxError: missing : after property id
- SyntaxError: missing ; before statement
- SyntaxError: missing = in const declaration
- SyntaxError: missing ] after element list
- SyntaxError: missing formal parameter
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- SyntaxError: missing } after property list
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- Warning: -file- is being assigned a //# sourceMappingURL, but already has one
- Warning: 08/09 is not a legal ECMA-262 octal constant
- Warning: Date.prototype.toLocaleFormat is deprecated
- Warning: JavaScript 1.6's for-each-in loops are deprecated
- Warning: String.x is deprecated; use String.prototype.x instead
- Warning: expression closures are deprecated
- Warning: unreachable code after return statement
- X.prototype.y called on incompatible type
- JavaScript technologies overview
- Lexical grammar
- Enumerability and ownership of properties
- Iteration protocols
- Transitioning to strict mode
- Template literals
- Deprecated features
- ECMAScript 2015 support in Mozilla
- ECMAScript 5 support in Mozilla
- Firefox JavaScript changelog
- New in JavaScript 1.1
- New in JavaScript 1.2
- New in JavaScript 1.3
- New in JavaScript 1.4
- New in JavaScript 1.5
- New in JavaScript 1.6
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- Documentation:
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Properties in JavaScript: definition versus assignment
Definition versus assignment.
Assignment. To assign to a property, one uses an expression such as
The following two sections go into more detail regarding how definition and assignment work. Feel free to skip them. You should still be able to understand Sect. 4, “The consequences”, and later.
Recap: property attributes and internal properties
Kinds of properties.
- Named accessor properties: A property that exists thanks to a getter or a setter.
- Named data properties: A property that h as a value. Those are the most common properties. They include methods.
- Internal properties: are used internally by JavaScript and not directly accessible via the language. However, there can be indirect ways of accessing them. Example: Every object has an internal property called [[Prototype]]. You cannot directly read it, but still retrieve its value, via Object.getPrototypeOf() . While internal properties are referred to by a name in square brackets, they are nameless in the sense that they are invisible and don’t have a normal, string-valued property name.
Property attributes
- [[Enumerable]]: If a property is non-enumerable, it can’t be seen by some operations, such as for...in and Object.keys() [2] .
- [[Configurable]]: If a property is non-configurable, none of the attributes (except [[Value]]) can be changed via a definition.
- [[Value]]: is the value of the property.
- [[Writable]]: determines whether the value can be changed.
- [[Get]]: holds a getter method.
- [[Set]]: holds a setter method.
Property descriptors
Internal properties
- [[Prototype]]: The prototype of the object.
- [[Extensible]]: Is this object extensible , can new properties be added to it?
- [[DefineOwnProperty]]: Define a property. See explanation below.
- [[Put]]: Assign to a property. See explanation below.
The details of definition and assignment
Defining a property.
[[ DefineOwnProperty ]] (P, Desc, Throw)
- If this does not have an own property whose name is P : Create a new property if the object is extensible, reject if it isn’t.
- Otherwise, there already is an own property and the definition changes that property.
- Converting a data property to an accessor property or vice versa
- Changing [[Configurable]] or [[Enumerable]]
- Changing [[Writable]]
- Changing [[Value]] if [[Writable]] is false
- Changing [[Get]] or [[Set]]
- Otherwise, the existing own property is configurable and can be changed as specified.
Two functions for defining a property are Object.defineProperty and Object.defineProperties . For example:
Assigning to a property
[[ Put ]] (P, Value, Throw)
- If there is a read-only property whose name is P somewhere in the prototype chain: reject.
- If there is a setter whose name is P somewhere in the prototype chain: call the setter.
- If there is no own property whose name is P : if the the object is extensible then create a new property. this.[[DefineOwnProperty]]( P, { value: Value, writable: true, enumerable: true, configurable: true }, Throw ) If the object is not extensible then reject.
- Otherwise, there is an own property named P that is writable. Invoke this.[[DefineOwnProperty]](P, { value: Value }, Throw) That updates the value of P , but keeps its attributes (such as enumerability) unchanged
The consequences
Assignment calls a setter in a prototype, definition creates an own property, read-only properties in prototypes prevent assignment, but not definition.
Definition. With definition, we want to create a new own property:
The assignment operator does not change properties in prototypes
- Methods: Allow methods to be patched, directly in the prototype, but prevent accidental changes via descendants of the prototype.
- Non-method properties: The prototype provides shared default values for descendants. One can override these values via a descendant, but not change them. This is considered an anti-pattern and discouraged. It is cleaner to assign default values in constructors.
Only definition allows you to create a property with arbitrary attributes
The properties of an object literal are added via definition, attributes of methods.
- If you want to create a new property, use definition.
- If you want to change the value of a property, use assignment.
- Prototypes as classes – an introduction to JavaScript inheritance
- JavaScript properties: inheritance and enumerability
- Fixing the Read-only Override Prohibition Mistake [a page on the ECMAScript wiki with background information on this issue]
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Destructuring Assignment in JavaScript
Destructuring Assignment is a JavaScript expression that allows to unpack of values from arrays, or properties from objects, into distinct variables data can be extracted from arrays, objects, and nested objects, and assigned to variables . In Destructuring Assignment on the left-hand side, we define which value should be unpacked from the sourced variable. In general way implementation of the extraction of the array is as shown below:
Example:
- Array destructuring:
- Object destructuring:
Array destructuring
Using the Destructuring Assignment in JavaScript array possible situations, all the examples are listed below:
Example 1: When using destructuring assignment the same extraction can be done using below implementations.
Example 2: The array elements can be skipped as well using a comma separator. A single comma can be used to skip a single array element. One key difference between the spread operator and array destructuring is that the spread operator unpacks all array elements into a comma-separated list which does not allow us to pick or choose which elements we want to assign to variables. To skip the whole array it can be done using the number of commas as there is a number of array elements.
Example 3: In order to assign some array elements to variable and rest of the array elements to only a single variable can be achieved by using rest operator (…) as in below implementation. But one limitation of rest operator is that it works correctly only with the last elements implying a subarray cannot be obtained leaving the last element in the array.
Example 4: Values can also be swapped using destructuring assignment as below:
Example 5: Data can also be extracted from an array returned from a function. One advantage of using a destructuring assignment is that there is no need to manipulate an entire object in a function but just the fields that are required can be copied inside the function.
Example 6: In ES5 to assign variables from objects its implementation is
Example 7: The above implementation in ES6 using destructuring assignment is.
Object destructuring
Example 1: The Nested objects can also be destructured using destructuring syntax.
Example 2: Nested objects can also be destructuring
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How to assign multiple variables at once in JavaScript?
Is there any way to perform multiple assignment in JavaScript like this:
which would be equivalent to this:
- multiple-assignment
- 3 If you want; var a = "one", b = "two"; – Volkan Yılmaz Commented Jul 16, 2016 at 13:45
5 Answers 5
In ES6 you can do it this way:
The above code is ES6 notation and is called array destructuring/object destructuring (if it's an object).
You provide the array on the right-hand side of the expression and you have comma-separated variables surrounded by square brackets on the left-hand side.
The first variable maps to the first array value and so on.
![define assignment in javascript nCardot's user avatar](https://i.sstatic.net/8Otyc.jpg?s=64)
- please add some more description to it, so that the answer is fully understandable – webdeb Commented Jul 16, 2016 at 13:50
- 1 If you are unsure about the technical term that you used here, then read and add it in your answer. developer.mozilla.org/en/docs/Web/JavaScript/Reference/… – Rajaprabhu Aravindasamy Commented Jul 16, 2016 at 13:51
- Its destructuring we can use array destructuring since we are talking about arrays – Piyush.kapoor Commented Jul 16, 2016 at 13:54
- var [a, b] = [1,2,3,4,5] – webdeb Commented Jul 16, 2016 at 13:56
- 2 Will this incur any overhead from constructing the right-side array? Or are interpreters smart enough to have a fast path when the right side is an array literal? – Will Chen Commented Jul 16, 2021 at 14:51
While you cannot do var a, b = "one", "two"; , and get them assigned to each variable in the respective order, you can do : var a, b; to initialize these variables as undefined .
You can also do var a, b = 'foo'; to assign b to 'foo', while initializing 'a' as undefined .
Object destructuring
looks like:
You will also see this in JavaScript to import members of a module :
Import multiple exports from module. This inserts both foo and bar into the current scope.
If you aren't absolutely married to the idea of the values being at the end of the statement, this works:
If you want to assign to variables that have already been declared, you can use the comma operator to make it a one-liner.
![define assignment in javascript Ryan's user avatar](https://i.sstatic.net/8ft1I.jpg?s=64)
I wanted to extend Ryan's answer - particularly when it comes to for loops. Normally one might write a for loop as:
As many contend, the interpretive nature of JS causes arr.length to be reevaluated on every loop - causing performance loss on large loops (depending on the nature of the upper-bound, e.g., a function ). When performance is paramount, they suggest iterating backward:
However, this approach will cause problems when order is relevant - not to mention being uncommon notation and unclear. To get around this problem, you can construct it thusly:
While not as succinct as a standard loop, it performs better whilest being easier to read than a reverse loop.
No you can not do this way. Javascript doesn't support this type of declaration
![define assignment in javascript Shobhit Walia's user avatar](https://i.sstatic.net/3wX5z.jpg?s=64)
- 2 Except that it does . – nnnnnn Commented Jul 16, 2016 at 13:53
- 3 I seems you live in ice age of JS in ES6 you can use Destructuring Assignment – Morteza Tourani Commented Jul 16, 2016 at 14:06
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COMMENTS
Use the correct assignment operator that will result in x being 15 (same as x = x + y ). Start the Exercise. Well organized and easy to understand Web building tutorials with lots of examples of how to use HTML, CSS, JavaScript, SQL, Python, PHP, Bootstrap, Java, XML and more.
Assignment (=) The assignment ( =) operator is used to assign a value to a variable or property. The assignment expression itself has a value, which is the assigned value. This allows multiple assignments to be chained in order to assign a single value to multiple variables.
This chapter describes JavaScript's expressions and operators, including assignment, comparison, arithmetic, bitwise, logical, string, ternary and more. At a high level, an expression is a valid unit of code that resolves to a value. There are two types of expressions: those that have side effects (such as assigning values) and those that ...
An assignment operator ( =) assigns a value to a variable. The syntax of the assignment operator is as follows: let a = b; Code language: JavaScript (javascript) In this syntax, JavaScript evaluates the expression b first and assigns the result to the variable a. The following example declares the counter variable and initializes its value to zero:
JavaScript Exponentiation Assignment Operator in JavaScript is represented by "**=". This operator is used to raise the value of the variable to the power of the operand which is right. This can also be explained as the first variable is the power of the second operand. The exponentiation operator is equal to Math.pow(). Syntax: a **= b or a = a **
An assignment operator assigns a value to its left operand based on the value of its right operand.. Overview. The basic assignment operator is equal (=), which assigns the value of its right operand to its left operand.That is, x = y assigns the value of y to x.The other assignment operators are usually shorthand for standard operations, as shown in the following definitions and examples.
In this tutorial, you will learn about all the different assignment operators in javascript and how to use them in javascript. Assignment Operators. ... In the following table if variable a is not defined then assume it to be 10. Operator Description Example Equivalent to = Assignment operator: a = 10: a = 10 += Addition assignment operator: a ...
The shorthand assignment operator += can also be used to concatenate strings. For example, var mystring = 'alpha'; mystring += 'bet'; // evaluates to "alphabet" and assigns this value to mystring. Conditional (ternary) operator. The conditional operator is the only JavaScript operator that takes three operands. The operator can have one of two ...
The basic assignment operator is equal ( = ), which assigns the value of its right operand to its left operand. That is, x = y assigns the value of y to x. The other assignment operators are usually shorthand for standard operations, as shown in the following definitions and examples. Name. Shorthand operator.
Here is an example: var a = 'quux'; a.foo = 'bar'; document.writeln(a.foo); This will output undefined: a holds a primitive value, which gets promoted to an object when assigning the property foo. But this new object is immediately discarded, so the value of foo is lost. Think of it like this: var a = 'quux';
JavaScript operators are special symbols that perform operations on one or more operands (values). In this tutorial, you will learn about JavaScript operators with the help of examples. ... JavaScript Assignment Operators. We use assignment operators to assign values to variables. For example, let x = 5; Here, we used the = operator to assign ...
Description. Logical AND assignment short-circuits, meaning that x &&= y is equivalent to x && (x = y), except that the expression x is only evaluated once. No assignment is performed if the left-hand side is not truthy, due to short-circuiting of the logical AND operator. For example, the following does not throw an error, despite x being ...
Assignment in a conditional statement is valid in javascript, because your just asking "if assignment is valid, do something which possibly includes the result of the assignment". But indeed, assigning before the conditional is also valid, not too verbose, and more commonly used. - okdewit.
The basic assignment operator is equal ( = ), which assigns the value of its right operand to its left operand. That is, x = y assigns the value of y to x. The other assignment operators are usually shorthand for standard operations, as shown in the following definitions and examples. Name. Shorthand operator.
Functions are one of the fundamental building blocks in JavaScript. A function in JavaScript is similar to a procedure—a set of statements that performs a task or calculates a value, but for a procedure to qualify as a function, it should take some input and return an output where there is some obvious relationship between the input and the output. To use a function, you must define it ...
Object.defineProperty(obj, propName, propDesc) The primary purpose of this function is to add an own (direct) property to obj, whose attributes (writable etc., see below) are as specified by propDesc. The secondary purpose is to change the attributes of a property, including its value. Assignment. To assign to a property, one uses an expression ...
There are two methods I know of that you can declare a variable's value by conditions. Method 1: If the condition evaluates to true, the value on the left side of the column would be assigned to the variable. If the condition evaluates to false the condition on the right will be assigned to the variable. You can also nest many conditions into ...
(4) Unless otherwise agreed to in writing by the mortgagee and mortgagor, the lien created by the assignment of rents is enforceable upon the mortgagor's default and written demand for the rents made by the mortgagee to the mortgagor, whereupon the mortgagor shall turn over all rents in the possession or control of the mortgagor at the time of the written demand or collected thereafter (the ...
Destructuring Assignment is a JavaScript expression that allows to unpack of values from arrays, or properties from objects, into distinct variables data can be extracted from arrays, objects, and nested objects, and assigned to variables. In Destructuring Assignment on the left-hand side, we define which value should be unpacked from the ...
The Object.assign() method only copies enumerable and own properties from a source object to a target object. It uses [[Get]] on the source and [[Set]] on the target, so it will invoke getters and setters. Therefore it assigns properties, versus copying or defining new properties.
12. While you cannot do var a, b = "one", "two";, and get them assigned to each variable in the respective order, you can do : var a, b; to initialize these variables as undefined. You can also do var a, b = 'foo'; to assign b to 'foo', while initializing 'a' as undefined. var a, b;
x ||= y. Description. Logical OR assignment short-circuits, meaning that x ||= y is equivalent to x || (x = y), except that the expression x is only evaluated once. No assignment is performed if the left-hand side is not falsy, due to short-circuiting of the logical OR operator. For example, the following does not throw an error, despite x ...