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ES6 Destructuring Assignment

Summary : in this tutorial, you will learn how to use the ES6 destructuring assignment that allows you to destructure an array into individual variables.

ES6 provides a new feature called destructing assignment that allows you to destructure properties of an object or elements of an array into individual variables.

Let’s start with the array destructuring.

Introduction to JavaScript Array destructuring

Assuming that you have a function that returns an array of numbers as follows:

The following invokes the getScores() function and assigns the returned value to a variable:

To get the individual score, you need to do like this:

Prior to ES6, there was no direct way to assign the elements of the returned array to multiple variables such as x , y and z .

Fortunately, starting from ES6, you can use the destructing assignment as follows:

The variables x , y and z will take the values of the first, second, and third elements of the returned array.

Note that the square brackets [] look like the array syntax but they are not.

If the getScores() function returns an array of two elements, the third variable will be undefined , like this:

In case the getScores() function returns an array that has more than three elements, the remaining elements are discarded. For example:

Array Destructuring Assignment and Rest syntax

It’s possible to take all remaining elements of an array and put them in a new array by using the rest syntax (...) :

The variables x and y receive values of the first two elements of the returned array. And the args variable receives all the remaining arguments, which are the last two elements of the returned array.

Note that it’s possible to destructure an array in the assignment that separates from the variable’s declaration. For example:

Setting default values

See the following example:

How it works:

  • First, declare the getItems() function that returns an array of two numbers.
  • Then, assign the items variable to the returned array of the getItems() function.
  • Finally, check if the third element exists in the array. If not, assign the value 0 to the thirdItem variable.

It’ll be simpler with the destructuring assignment with a default value:

If the value taken from the array is undefined , you can assign the variable a default value, like this:

If the getItems() function doesn’t return an array and you expect an array, the destructing assignment will result in an error. For example:

A typical way to solve this is to fallback the returned value of the getItems() function to an empty array like this:

Nested array destructuring

The following function returns an array that contains an element which is another array, or nested array:

Since the third element of the returned array is another array, you need to use the nested array destructuring syntax to destructure it, like this:

Array Destructuring Assignment Applications

Let’s see some practical examples of using the array destructuring assignment syntax.

1) Swapping variables

The array destructuring makes it easy to swap values of variables without using a temporary variable:

2) Functions that return multiple values

In JavaScript, a function can return a value. However, you can return an array that contains multiple values, for example:

And then you use the array destructuring assignment syntax to destructure the elements of the return array into variables:

In this tutorial, you have learned how to use the ES6 destructuring assignment to destructure elements in an array into individual variables.

How Destructuring Works in JavaScript – Explained with Code Examples

Sahil Mahapatra

Destructuring is a powerful JavaScript feature introduced in ES6 (ECMAScript 2015). It makes it easier to extract values from arrays or properties from objects and assign them to variables in a readable way.

Let's delve into how destructuring works and explore various use cases with examples.

You can get the source code from here .

Table of Contents

  • What is Destructuring ?

Array Destructuring

Object destructuring, what is destructuring.

Destructuring is a technique that allows you to unpack values from arrays or objects into separate variables.

This process involves breaking down complex data structures into simpler parts, making it easier to work with them.

Let's start with array destructuring. We'll use the following example.

Without destructuring, extracting values from an array can be verbose:

Here, you're accessing each element of the hobbies array using index notation and assigning them to individual variables.

Destructuring simplifies this process into a single line of code, like this:

In this example, you're extracting the values from the hobbies array and assigning them to variables firstHobby , secondHobby , and thirdHobby , respectively.

Skipping Elements from the Array

You can choose to ignore certain elements by omitting them from the destructuring pattern:

In this example, you're destructuring the hobbies array but only assigning values to the firstHobby and thirdHobby variables. You're skipping the second element in the array by placing a comma without a variable name between firstHobby and thirdHobby . This allows you to extract specific elements from the array while ignoring others, providing more flexibility and control in your destructuring patterns.

Nested Array Destructuring

Array destructuring can also be nested. Here's an example:

In this code, we have a nested array nestedArray . Using nested array destructuring, you're extracting values from both the outer and inner arrays and assigning them to variables firstValue , secondValue , thirdValue , and fourthValue .

Moving on to object destructuring, consider the following object:

Regular Destructuring

Object destructuring allows you to extract properties from objects:

In this example, { name, age, city } is the destructuring syntax. It means you're extracting the name , age , and city properties from the person object and assigning them to variables of the same name. So name will have the value "John Doe" , age will have 30 , and city will have "New York" .

Destructuring with Different Names

You can assign extracted properties to variables with different names:

In this example, you're using a syntax like { name: personName, age: personAge, city: personCity } which allows you to assign extracted properties to variables with different names. Here, name from the person object is assigned to personName , age is assigned to personAge , and city is assigned to personCity .

Having Default Values while Destructuring

You can also provide default values for object properties:

Here, you're providing a default value "Unknown" for the gender property in case it's not present in the person object. If gender is not defined in person , the variable gender will default to "Unknown" .

Nested Objects

Object destructuring supports nested objects:

In this example, { name, address: { city, country } } is the destructuring syntax. You're extracting the name property directly from the person object. Then within the address object, you're extracting the city and country properties. So city will have the value "New York" , and country will default to undefined assuming address does not have a country property.

That's it! You should now have a good understanding of how JavaScript destructuring works for arrays and objects.

Feel free to experiment with the code examples to further solidify your understanding. If you have any feedback or questions, please contact me on Twitter or Linkedin . Happy learning!

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JavaScript Destructuring Assignment

  • JavaScript Destructuring

The destructuring assignment introduced in ES6 makes it easy to assign array values and object properties to distinct variables . For example, Before ES6:

Note : The order of the name does not matter in object destructuring.

For example, you could write the above program as:

Note : When destructuring objects, you should use the same name for the variable as the corresponding object key.

For example,

If you want to assign different variable names for the object key, you can use:

  • Array Destructuring

You can also perform array destructuring in a similar way. For example,

  • Assign Default Values

You can assign the default values for variables while using destructuring. For example,

In the above program, arrValue has only one element. Hence,

  • the x variable will be 10
  • the y variable takes the default value 7

In object destructuring, you can pass default values in a similar way. For example,

  • Swapping Variables

In this example, two variables are swapped using the destructuring assignment syntax.

You can skip unwanted items in an array without assigning them to local variables. For example,

In the above program, the second element is omitted by using the comma separator , .

Assign Remaining Elements to a Single Variable

You can assign the remaining elements of an array to a variable using the spread syntax ... . For example,

Here, one is assigned to the x variable. And the rest of the array elements are assigned to y variable.

You can also assign the rest of the object properties to a single variable. For example,

Note : The variable with the spread syntax cannot have a trailing comma , . You should use this rest element (variable with spread syntax) as the last variable.

  • Nested Destructuring Assignment

You can perform nested destructuring for array elements. For example,

Here, the variable y and z are assigned nested elements two and three .

In order to execute the nested destructuring assignment, you have to enclose the variables in an array structure (by enclosing inside [] ).

You can also perform nested destructuring for object properties. For example,

In order to execute the nested destructuring assignment for objects, you have to enclose the variables in an object structure (by enclosing inside {} ).

Note : Destructuring assignment feature was introduced in ES6 . Some browsers may not support the use of the destructuring assignment. Visit Javascript Destructuring support to learn more.

Table of Contents

  • Skipping Items
  • Arbitrary Number of Elements

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  • Destructuring assignment

Unpacking values from a regular expression match

Es2015 version, invalid javascript identifier as a property name.

The destructuring assignment syntax is a JavaScript expression that makes it possible to unpack values from arrays, or properties from objects, into distinct variables.

Description

The object and array literal expressions provide an easy way to create ad hoc packages of data.

The destructuring assignment uses similar syntax, but on the left-hand side of the assignment to define what values to unpack from the sourced variable.

This capability is similar to features present in languages such as Perl and Python.

Array destructuring

Basic variable assignment, assignment separate from declaration.

A variable can be assigned its value via destructuring separate from the variable's declaration.

Default values

A variable can be assigned a default, in the case that the value unpacked from the array is undefined .

Swapping variables

Two variables values can be swapped in one destructuring expression.

Without destructuring assignment, swapping two values requires a temporary variable (or, in some low-level languages, the XOR-swap trick ).

Parsing an array returned from a function

It's always been possible to return an array from a function. Destructuring can make working with an array return value more concise.

In this example, f() returns the values [1, 2] as its output, which can be parsed in a single line with destructuring.

Ignoring some returned values

You can ignore return values that you're not interested in:

You can also ignore all returned values:

Assigning the rest of an array to a variable

When destructuring an array, you can unpack and assign the remaining part of it to a variable using the rest pattern:

Note that a SyntaxError will be thrown if a trailing comma is used on the left-hand side with a rest element:

When the regular expression exec() method finds a match, it returns an array containing first the entire matched portion of the string and then the portions of the string that matched each parenthesized group in the regular expression. Destructuring assignment allows you to unpack the parts out of this array easily, ignoring the full match if it is not needed.

Object destructuring

Basic assignment, assignment without declaration.

A variable can be assigned its value with destructuring separate from its declaration.

The ( .. ) around the assignment statement is required syntax when using object literal destructuring assignment without a declaration.

{a, b} = {a: 1, b: 2} is not valid stand-alone syntax, as the {a, b} on the left-hand side is considered a block and not an object literal.

However, ({a, b} = {a: 1, b: 2}) is valid, as is var {a, b} = {a: 1, b: 2}

NOTE: Your ( ..) expression needs to be preceded by a semicolon or it may be used to execute a function on the previous line.

Assigning to new variable names

A property can be unpacked from an object and assigned to a variable with a different name than the object property.

A variable can be assigned a default, in the case that the value unpacked from the object is undefined .

Setting a function parameter's default value

Es5 version, nested object and array destructuring, for of iteration and destructuring, unpacking fields from objects passed as function parameter.

This unpacks the id , displayName and firstName from the user object and prints them.

Computed object property names and destructuring

Computed property names, like on object literals , can be used with destructuring.

Rest in Object Destructuring

The Rest/Spread Properties for ECMAScript proposal (stage 3) adds the rest syntax to destructuring. Rest properties collect the remaining own enumerable property keys that are not already picked off by the destructuring pattern.

Destructuring can be used with property names that are not valid JavaScript identifiers  by providing an alternative identifer that is valid.

Specifications

Browser compatibility.

[1] Requires "Enable experimental Javascript features" to be enabled under `about:flags`

Firefox-specific notes

  • Firefox provided a non-standard language extension in JS1.7 for destructuring. This extension has been removed in Gecko 40 (Firefox 40 / Thunderbird 40 / SeaMonkey 2.37). See bug 1083498 .
  • Starting with Gecko 41 (Firefox 41 / Thunderbird 41 / SeaMonkey 2.38) and to comply with the ES2015 specification, parenthesized destructuring patterns, like ([a, b]) = [1, 2] or ({a, b}) = { a: 1, b: 2 } , are now considered invalid and will throw a SyntaxError . See Jeff Walden's blog post and bug 1146136 for more details.
  • Assignment operators
  • "ES6 in Depth: Destructuring" on hacks.mozilla.org

Destructuring assignment

We have an object:

Write the destructuring assignment that reads:

  • name property into the variable name .
  • years property into the variable age .
  • isAdmin property into the variable isAdmin (false, if no such property)

Here’s an example of the values after your assignment:

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JavaScript Destructuring [In-Depth Tutorial]

January 7, 2023

Getting started with JavaScript Destructuring

JavaScript destructuring is a powerful feature that allows developers to extract values from objects and arrays and assign them to variables. It can greatly simplify and improve the readability of your code, particularly when working with complex data structures.

There are several approaches to destructuring in JavaScript, each with its own strengths and use cases. These approaches include destructuring arrays, destructuring objects, and destructuring function arguments.

Consider this syntax:

That code destructures first by copying it from  obj  (extracting it from the object structure).

In this article, we will explore each of these approaches in detail and discuss when and how to use them effectively in your code.

Simple Examples to understand the concept

As stated earlier, JavaScript destructuring is a way to extract values from arrays, or properties from objects, and assign them to variables. It is a concise way to create variables from data stored in objects and arrays.

For example, consider the following array:

To extract the values from this array and assign them to separate variables, you could do something like this:

This works, but it can get cumbersome when you have large arrays or when you need to extract values from nested arrays or objects.

Here's where destructuring comes in handy. You can extract values from arrays or properties from objects and assign them to variables using a syntax that looks like this:

This creates three variables, color1 , color2 , and color3 , and assigns them the values of the corresponding elements in the colors array.

You can also use destructuring to extract values from nested arrays or objects.

This creates two variables, user1 and user2 , and assigns them the values of the name property of the objects in the data array.

Let’s show more destructuring examples

Destructuring objects

The new syntax gives you a new way to destructure things, usually with less repetition and fewer unnecessary variables. So. instead of writing:

you can write:

Example-1:  You can use destructuring to extract values from objects and assign them to variables. Let’s illustrate this by destructing a person object.

Example-2: You can also use destructuring to extract values from nested objects. As long as you know the structure of the nested objects, you can easily define them within the destructuring assignment. Here is an example of how to work with destructing in nested objects.

Example-3: Take a look at the following object:

We have an object called  chair , and it contains a bunch of properties. If we want to extract and store the values of just the  brand  and  price  properties, we can do so via destructuring:

In our variable declaration and assignment, we are declaring two variables called  brand  and  price  whose names match the property names inside the object we are unpacking. The end result is that we are able to work with the values stored by  brand  and  price  properties as their own individual variables.

If we wanted to access the remaining properties without any manual bookkeeping, the spread operator exists in this context as well:

The rest variable stores the results of destructuring our object using the spread operator . What gets returned is a new object whose properties are the ones we haven’t unpacked. In other words, this new object contains everything except the brand and price properties.

Destructuring Arrays

You can destructure arrays and other iterables, too. Unsurprisingly, the syntax uses square brackets ( [] ) instead of the curly braces ( {} ) used by object destructuring:

The value each target receives depends on where it is in the pattern. So with  [first, second] ,  first  gets the value from  arr[0]  because it's in the 0th position, and second gets the value from  arr[1]  because it's in the 1st position. It's just like you'd written:

It's valid to leave out elements you don't want. Notice that the following code has no variable in the 0th position:

You can leave gaps in the middle, too:

Consider this array:

If we want to store the first three items from the array in their own variables, here is how we can do that by using destructuring:

To print out the remaining items we can use spread operator ( ... ):

How to skip items with comma?

We can see in our examples for array that each variable is comma-separated, and the comma helps indicate when we jump from one item in our array to the next in sequential order.

So what if we want to skip an item from being assigned to a variable. To skip an item (or many items), we need to specify a comma but no variable to pair with the comma.

Take a look at the following example:

Notice that we specify an empty comma after the a variable. This ends up appearing as two commas, and the result is one where we map only the first item and the third item. The second item is skipped since there is no variable to store that item.

How to handle more variables then actual data?

Sometimes we may be trying to map more variables than there is data to map to them. Take a look at the following example:

The array we are trying to unpack into variables only has two items, but we have three variables. When we have a variable that doesn’t have any data associated with it, that variable is given a value of undefined.

If the undefined value is undesirable, we can specify a default value to override that behavior:

In this variation, notice that the value for third is set to the default value of  Person  because it doesn’t have a defined value in the array.

Difference between destructuring Arrays and Objects

The destructuring assignment for arrays involves brackets:

The destructuring assignment for objects involves curly braces:

  • With arrays, the order of our variable names during assignment mapped to the order of our items in the array. With objects, order doesn’t matter. The variable names determine which of our object property values get mapped.
  • With arrays, the spread operator returns a new array whose contents are a consecutive list of array values starting right after the ones we had already mapped. With objects, the spread operator returns a new object made up of the properties we haven’t already mapped. The order of how the properties are defined inside the object doesn’t matter. The only thing that matters is which properties have already been mapped and which ones haven’t.

Destructuring function arguments

You can use destructuring to extract values from function arguments. Let’s illustrate this scenario by creating a simple hello function that takes an object.

Destructuring in for-of loops

You can use destructuring in for-of loops to extract values from arrays or objects. If we want to loop through an object values, we can easily use the destructing to loop through it concisely. Let’s look through the example below.

In the code, the for-of loop iterates over the elements of the data array and uses destructuring to extract the id and name properties from each object. The destructured variables id and name are then used in the loop body to log a message to the console that includes the name and id of each object.

Destructuring is a powerful tool that can greatly simplify your code and make it more readable. It is widely used in modern JavaScript development and is a good tool to have in your toolbox. We can use it with arrays, objects, functions and loops to make concise code. Even if you and I have no plans of ever using it in our code, destructuring has gotten so common (especially in frameworks like React and Vue) that we’ll find ourselves forced to use it or needing to review/read code written by someone else that heavily relies on it.

Destructuring assignment - JavaScript | MDN (mozilla.org)

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Efficient Coding with JavaScript Object Destructuring: A Practical Guide

Introduction to javascript object destructuring.

JavaScript Object Destructuring is a powerful feature that was introduced with ES6, simplifying the process of extracting data from objects and arrays. This technique enables developers to write cleaner and more efficient code, making it easier to read and maintain.

In this article, we'll dive deep into the world of object destructuring, exploring its various use cases, and sprinkling in some humor along the way. So, buckle up and get ready to level up your JavaScript skills!

Basic Object Destructuring

Let's start by understanding the fundamentals of object destructuring . It's a shorthand syntax that allows us to extract properties from an object and assign them to variables. Here's a basic example to show the concept:

In the code snippet above, we've used object destructuring to extract the name , alterEgo , and powers properties from the superhero object. The syntax is straightforward: we enclose the property names we want to extract within curly braces {} and assign the resulting expression to the source object. VoilĂ ! We've got our variables ready for action, just like our friendly neighborhood Spider-Man.

discover destructuring assignment concept

Destructuring with Default Values

Sometimes, the object we're destructuring might not have all the properties we're trying to extract. In such cases, we can provide default values for these missing properties to prevent our code from breaking. Check out this example to see how it's done:

In the example above, we're destructuring the musician object. However, the band property is missing. To handle this gracefully, we've provided a default value, 'Queen' , for the band property in the destructuring assignment. Now, when we try to access the band variable, it returns the default value instead of undefined . Isn't that rockin' ?

Nested Object Destructuring

What if we have an object with nested properties we want to extract? Fear not, nested object destructuring is here to save the day! This technique allows us to extract properties from nested objects using a similar syntax. Let's dive into an example:

In this example, we've used nested object destructuring to extract properties from the student object, which has a nested address object. By using nested curly braces {} in the destructuring assignment, we can access properties within nested objects, making our code cleaner and easier to read. It's like unpacking a Russian nesting doll of code, one layer at a time!

Array Destructuring

So far, we've focused on destructuring objects, but we can also apply similar techniques to arrays . In fact, ES6 introduced a handy syntax for array destructuring that makes it a breeze. Let's take a look at a simple example:

In the example above, we've used array destructuring to assign the elements of the colors array to individual variables. Instead of curly braces {} , we use square brackets [] to enclose the variables in the destructuring assignment. This way, we can easily access each element of the array without needing to use their index positions.

Pro tip: You can also use the rest syntax ( ... ) to gather the remaining elements of an array into a new array. For example:

Array destructuring is a colorful addition to our JavaScript toolbox, providing a concise and efficient way to work with arrays.

Flying Man

Destructuring Function Parameters

Another fantastic use of destructuring is in function parameters . It can help us make our functions more flexible and improve their readability. Let's take a look at how we can use object destructuring in function parameters:

In the example above, we've defined a greet function with a destructured object parameter. When we call the function with the person object, the function automatically extracts the required properties ( name , age , and city ) from the object.

As a bonus, we can also provide default values for destructured function parameters:

With destructuring in function parameters, we've got a powerful tool to write cleaner, more flexible, and more readable functions. It's like having a Swiss Army knife in our JavaScript arsenal!

Real-World Use Cases

Now that we've explored the various aspects of destructuring, let's examine some real-world use cases where this technique can make a significant difference in our code:

Extracting data from API responses : When working with APIs, we often need to extract specific data from the received response. Destructuring can help us achieve this in a clean and concise manner:

Simplifying Redux reducers : When working with Redux, destructuring can help simplify our reducers by making it easier to update the state:

Managing component props in React : In React, destructuring can help us manage component props more efficiently and improve readability:

These examples illustrate just a few of the many ways destructuring can enhance our JavaScript code in real-world scenarios. Once you use destructuring, you'll wonder how you ever lived without it!

Common Pitfalls and Tips

As powerful as destructuring is, it's essential to be aware of some common pitfalls and tips to ensure we're using it effectively:

Watch out for naming conflicts : When destructuring objects, make sure there are no naming conflicts between the extracted variables and existing variables in the same scope. If conflicts arise, consider using aliases to rename the extracted variables:

Avoid overusing destructuring : While destructuring can make our code more concise, overusing it can also make our code harder to read. Use it judiciously and avoid destructuring too many nested levels at once.

Be mindful of the order in array destructuring : When destructuring arrays, the order of the variables matters. Align your variables with the correct array elements. Use empty spaces to skip unwanted elements:

Combining object and array destructuring : Remember that you can combine object and array destructuring when working with complex data structures:

By keeping these tips and pitfalls in mind, you can wield the power of destructuring effectively and responsibly, turning your code into a well-oiled JavaScript machine.

In this article, we've explored the ins and outs of JavaScript Object Destructuring and its various applications, including basic and nested object destructuring, default values, array destructuring, and destructuring in function parameters. We've also delved into real-world use cases and provided tips to avoid common pitfalls.

With destructuring in your JavaScript toolbelt, you're now equipped to write cleaner, more efficient, and more readable code. So, go forth and destructure like a pro, and remember: with great destructuring power comes great responsibility!

Happy coding, and may your code always be bug-free (or at least close to it)!

Beyond the Basics: Unleashing the Power of JavaScript Array Methods for Expert Developers

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Understanding object destructuring in javascript: a beginner's guide.

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Table of contents

Introduction, assigning values to variables, skipping elements, setting default values, destructuring with rest operator, renaming variable, using the rest syntax.

Object destructuring is an important technique in JavaScript that enables developers to easily extract specific properties from an object and assign them to variables with a single line of code. This not only simplifies the code but also improves its readability and maintainability.

Introduced in ECMAScript 6 (ES6), object destructuring is one of several features aimed at enhancing the language's expressiveness and functionality. The use of curly braces ( {} ) is employed in ES6 to extract properties from objects and assign them to variables with the same name. Before ES6, developers had to manually extract properties from objects by writing multiple lines of code. The syntax for object destructuring is clear and concise and can be used for both simple and nested objects, as well as for default values and aliasing.

For beginners, comprehending the concept of object destructuring in JavaScript can be quite challenging and can also hinder their ability to understand code that uses this technique. In this tutorial, you will learn how to effectively destructure arrays and object literals in JavaScript.

We will begin by first learning how to destructure arrays, before moving on to object literals.

Destructuring Array Literals

By using the destructuring assignment syntax, we can efficiently extract the elements we want from an array and assign them to new variables in a readable and concise manner. This approach enables us to access relevant data swiftly and avoid the use of verbose and repetitive indexing code. In this section, we will examine different methods of destructuring array literals.

The process of assigning values to variables is pretty straightforward. We start by declaring a variable on the left-hand side of the assignment operator ( = ), followed by an array on the right-hand side. Each variable on the left-hand side corresponds to an element of the array on the right-hand side. Consider the following example:

In the above code, the pattern [first, second, third] matches the first three elements of the countries array and assigns their values to the variables: first , second , and third , respectively. The square brackets on the left side of the equal sign define the variables that will receive the values. The remaining elements of the array ('USA', 'China', 'England', and 'India') are not assigned to any variables.

In the example above, we skipped 'USA', 'China', 'England', and 'India' by omitting the corresponding variable name. You can also skip elements by using commas to indicate their position in the array. For example:

In this code, the first element of the countries array is assigned to the variable northAmerica , which means that northAmerica now contains the string "Canada". The third element of the countries array is assigned to the variable Africa , which means that Africa now contains the string "Nigeria". The second and fourth elements of the array are skipped due to the blank space in between the commas.

When an array has undefined or missing elements, it is helpful to assign default values while destructuring it. This way, the default values can provide fallbacks if the array does not have the expected values or they are undefined. For example, consider the following code:

In the code above, the default values are assigned to the variables when the corresponding value in the array is missing or undefined. The first variable first will be assigned the value of the first element in the countries array, which is 'Canada'. Similarly, the second variable will be assigned the value of the second element in the array, which is 'Lesotho'. Since the third element in the array is missing, the default value 'Nigeria' will be assigned to the third variable. Finally, the fourth variable will be assigned the default value which is 'Australia' because the fourth element in the array is undefined .

The rest operator is denoted by three dots ( ... ) and can only be used as the last element in an array destructuring statement. When used, it collects all the remaining elements of the array that were not assigned to individual variables and assigns them to the variable that follows the rest operator. The rest operator essentially allows developers to create a new array from the remaining elements of an existing array.

Consider the following example:

In this example, the first two elements of the countries array are assigned to the northAmerica and Africa variables, respectively. The rest operator is then used to collect the remaining elements of the array [ 'Nigeria', 'USA', 'China', 'England', 'India' ] and assign them to the remainings variable.

Destructuring Object Literals

Destructuring array literals differs slightly from dealing with object literals. In an array, objects are indexed with a numerical value starting from 0, while object literals are indexed using keys. When destructuring an object in an array, the syntax involves using square brackets to access the index of the object you want to extract. When destructuring object literals, the syntax involves using curly braces to access the key of the property you want to extract.

By assigning values to variables in object destructuring, you can extract specific properties from an object and assign them to variables with the same names. Consider the following example:

In this example, we extracted the values of the northAmerica and asia properties from the countriesByContinent object and assign them to new variables with the same names. This means that the values of the northAmerica and asia properties are now stored in the northAmerica and asia variables, respectively.

Before object destructuring was introduced in JavaScript, you would need to access object properties using the dot notation or square bracket notation to extract their values. For example, to access the values of the northAmerica and asia properties in the countriesByContinent object without destructuring, you would do it like this:

Sometimes, it may be necessary to rename a variable in object destructuring to avoid conflicts in cases where the variable already exists in your code. If you already have a variable with the same name as a property you are trying to extract, it can cause conflicts and lead to unexpected results. To avoid this, you will need to rename the extracted property and assign it to a new variable with a different name.

Consider the code below:

In this code, we extract the values of the australia and africa properties from the countriesByContinent object and assign them to new variables oceania and motherland , respectively.

Similar to array destructuring, we can also define default values for properties in object destructuring. This is useful when some properties are missing from the object, or if their values are undefined, as the default values can act as fallbacks.

Let's consider the following code below:

In the example above, europe will be assigned the value "England" because the europe property is present in the countriesByContinent object. northAmerica will be assigned the value "Canada" because that is the value of the northAmerica property in the object.

However, the africa and asia properties are not present in the countriesByContinent object. Therefore, their default values of "Ghana" and "India" , respectively, will be used instead.

The rest syntax used in object destructuring functions similarly to its use in array destructuring. This syntax is used to gather the remaining properties of an object and store them in a new object variable. It involves using the three dots ( 
 ) followed by the name of a variable within the curly braces {} .

Let's consider the example below:

The ...rest syntax is used to collect all the remaining properties of the countriesByContinent object that has not been assigned to europe or northAmerica . In this case, remainings will be a new object that contains the africa , asia , and southAmerica properties and their corresponding values.

Destructuring is an interesting concept in JavaScript that allows values to be extracted from arrays or objects. Although it can be very simple at first, destructuring has the potential to become very complex quite rapidly. That is why it is very important to maintain simplicity and readability when implementing destructuring in your code. Doing so will benefit both the developer and anyone who may review the code in the future, as well as make it easier to understand and maintain.

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What is a Destructuring assignment and explain it in brief in JavaScript ?

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The Destructuring assignment is the important technique introduced in ECMAScript 2015 (ES6) version of JavaScript that provides a shorthand syntax to extract or unpack array elements or properties of an object into distinct variables using a single line of code. In other words, this assignment helps us to segregate data of any iterable as well as non-iterable object and then helps us to use that segregated data individually on need or demand. It makes the code shorter and more readable.

Let us have a look over the below mentioned syntax of Destructuring assignment which will help us to reduce our code and make it more readable and scalable too. 

Syntax: The left-hand side of the expression of Destructuring assignment contains the distinct variables which actually defines what properties/values are to be unpacked or segregated from the source variable (or an array or an object) and the right-hand side specifies the corresponding object or array to which we are about to extract our data (the source variable which could be any iterable or non-iterable object). 

Example 1: The following example showcases the usage of extracting required array elements into distinct variables using Array Destructuring and will also help you to understand how Destructuring can be used to write clean and concise code.

Example 2: The spread operator is also used to unpack array elements but the main difference between Array Destructuring and spread operator is that spread unpacks all the array elements and this spread operator doesn’t allow us to skip or choose elements according to our requirement. Using Array Destructuring, we can skip the elements which are not required by using a ‘comma separator.’

Example 3: In the following example, an address object is de-structured to obtain only the city and sector properties and display the output on the console. 

Object Destructuring is an important feature of JavaScript and is very useful when only certain properties of an object are to be used and the complete object is not required or  not in consideration. This feature of ES6 is commonly used in JavaScript frameworks and its main application is parameter de-structuring i.e. objects passed into function parameters can be de-structured before use, according to the function requirement.

Note: The order of name doesn’t matter in case we are implementing Object Destructuring in JavaScript.

For example, in the above illustrated example, if we change the order of names in which the particular object’s properties has been de-structured from the source object, then also our task will be same and result would also be the same. Let us see the implementation of this illustrated fact below (with the help of following code snippet):

Example 4: Object properties can also be extracted using a different variable name (an alias) other than the property name defined in the source object. The following example uses aliases to extract the values of state and city properties from the address object.

Example 5: A nested object i.e. an object within the source object can also be de-structured using the same syntax of Object Destructuring to access only the properties required. The example below contains an address object having a nested object pin which is de-structured to extract only the pin-code of the address.

Example-6: In this example we will try to understand how actually setting function parameter’s default value task works. In other words using the below mentioned code snippet we will try to understand how we may set a function parameter’s default value.

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ES6: Use Destructuring Assignment to Assign Variables from Objects help

I am trying to solve the Destructuring Assignment challenge and I am stuck.

Can someone explain the destructuring assignment concept and walk me through the challenge please?

Use destructuring to obtain the length of the input string str, and assign the length to len in line.

Starting code snippet:

I will go through the destructuring assignment concept itself, then cover up the challenge afterwards:

Destructuring assignment: a reintroduction

The destructuring assignment syntax is a JavaScript expression that makes it possible to unpack values from arrays, or properties from objects, into distinct variables.

“Come again? I don’t get your MDN copy-paste explanation
”

You see, arrays have values , and objects contain properties .

We usually access the array values and object properties like so:

And sometimes, we would like to assign those values into variables:

Now, the JavaScript community got jealous from Python (py already implements assignment destructuring) and decided to embrace the practice of clarity and an easier way to access data:

“But what if I want to rename type or color differently when I destructure the car object?”

Good catch, you can do that using the following syntax:

Along the way while using the assignment destructuring syntax you will find many gotchas, which you will need to read the syntax documentation carefully and patiently to get over them. I’d recommend MDN web docs - Destructuring assignment after understanding the basics.

“But why the extra syntactic sugar ?”

Because this way, you won’t need to repeat the destructured expression. It will also make some things easier to read. Consider the following example:

On the server-side, sometimes you need to get the username, email and password from a request object – let’s say the user is registering a new account – Instead of:

Or a little bit more complex, sometimes I only need certain properties from an object passed to a function: (or maybe I just want to pre-destruct the argument)

In more complex situations, this will save you an extra variable + improve readability . Now that you got this off, have a walk or a small break before going into the next section of this answer if you want. (solving the challenge)

Solving the destructuring assignment challenge

I think most people are confused partially because the lesson and challenge itself can be a bit unclear for new JavaScript programmers.

What the challenge is trying to say here:

The String global object contains a length property ( string.length ) that you can access when you create a new String . Assume a String is always passed to getLength(str) function. Use the destructuring assignment to assign the length property of String to len .

Can you now solve the challenge using the given code snippet?

If not, I don’t blame you, what makes this challenge unpleasantly confusing is the starting code snippet. Here is a better starting code snippet:

Now try to solve the above using the given challenge explanation; Use the destructuring assignment to assign the length property of String to len instead of accessing the str.length property and assigning it to len .

We’ve done something similar with the car’s example in the reintroduction section. Give it a couple of shots before reading the previous section again.

That’s a top notch explanation about Destructuring Assigments that I was going nuts about! Thank you.

I’d also like to add the following challenge information:

That may help more people reassigning values.

AGGGGGHHHHHH!!!

This felt like it should have been easy but I ended up taking a long time to work this one out.

Key to this on is that the string is the object, once you get that the whole thing makes a bit more sense.

Also try here:

After 1.22 of watching I had the answer.

:confused:

I’m still not getting it. Once I (finally) understood that every string is an object with property length , I came up with:

I feel like this should be working, but I’ve still got it wrong. I’m getting “len is not defined”. Well, duh, I’m trying to define it. What am I misunderstanding?

You’re close, you are unpacking the object and assigning the variable the other way around: (You’re probably getting "len is undefined." error as a result)

The correct syntax for assigning to new variable names :

Read this section again: (updated)

Whoops! Yeah, that was a silly mistake. I think I had it backwards because of how you normally assign values to variables. Thanks for the clarification and all of your help on this!

This one took me a long time to complete.

Thanks to U-ways and Jcunningham77 for explaining this one in the way I needed.

AGGGGGHHHHHH!!! This felt like it should have been easy but I ended up taking a long time to work this one out. Key to this on is that the string is the object, once you get that the whole thing makes a bit more sense.

This was the key. Truly. Realizing that the str is an object and as such using length as a key:value pair to put into len was what really took FOREVER and lots of research to finally understand.

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TechExchange Quick-Tip: The Benefits of Using JavaScript Destructuring Assignments in Custom Components

discover destructuring assignment concept

article by Frank Nimphius, June 2019

ES 6, known as ECMA Script 2015 or JavaScript 6, introduced the concept of destructuring for creating variables and assigning values to them. Destructuring, as an expression, reads values ​​from arrays and objects and assigns them to variables. Custom components in Oracle Digital Assistant support JavaScript destructuring and custom component developers may use this syntax to assign component input parameter values to variables. This article explains destructuring variable-assignments in custom components and points out the benefits.

Using Destructuring  in Custom Components

Destructuring in JavaScript works with arrays and objects. Input parameters defined on a custom component are passed as an object returned by the custom component SDK's   conversation.properties() function. Using the default component template* ) of the Oracle Bots Node SDK , you see the following content generated for your new custom component. 

const { human } = conversation.properties();

What this code does is, it uses destructuring to create a new constant variable with the name  human  and populates it  with the value of the "human" property in the object response of a call to the conversation.properties() function. Another way of writing above assignment would be using the traditional way:

const human = conversation.properties().human;

But if the above works, why changing it? Well, destructuring  comes with some benefits:

  • Less code to write
  • Easier to read
  • Ability to set default values  (!) for input parameters
  • Ease of assigning variable names different from the input parameter name

*) You can customize the default component template used by the  Oracle Bots Node SDK , following this Oracle TechExchange .

Using Destructuring to Set Default Values

Input parameters are defined in the custom component metadata() function as shown below. 

metadata: () => ({

The metadata section does not allow you to define default values for parameters. So despite that all except one parameter are marked as optional, there is no way to define a default value. Here destructuring becomes very handy. If, for example, the age property should be defaulted to 18, then you could use the following assignment. 

const { age = 18 } = conversation.properties();

Or, if you wanted to default the mail input to [email protected]

  const { mail = '[email protected]' } = conversation.properties();

The "traditional" equivalent of this code would be

const mail = conversation.properties().mail ? conversation.properties().mail : '[email protected]' ;

Still you may be a fan of the "traditional" style and don't bother the extra characters to write. But, lets then have a look how destructuring can populate two variables at once

const { age = 18, mail = '[email protected]' } = conversation.properties();

Handling the "Zero Input-Parameters" Case

Now that - hopefully - you are convinced of destructuring for variable assignments, you need to be made aware of a special situation, which is when no input parameters are passed by the bot designers (and I am not talking about passing null values for an input parameter).  For example, the following custom component definition 

Allows the custom component to be referenced in BotML as 

discover destructuring assignment concept

But wait. The variable property is flagged as "required", so how can no input parameter be passed? Well, the "required" setting matters to the validator in the BotML designer. So pressing the validate button in the dialog flow builder shows the following error:

discover destructuring assignment concept

Still, bot designers may decide to ignore the problem and release the skill. At runtime, the "required" statement does not cause an error unless the custom component developer checks if required parameters got a value and if not throws an error.

But, let's get back to the use case in which no input parameter is provided for a component. In this case the properties() function is not getting exposed on the conversation object in the custom component code and destructuring cannot be performed. To handle this case, you need to add some code that checks the existence of the properties() function. The code below defines a _default object that holds the values of the default values. Later, the assignment uses  conversation.properties() || _defaults to either assign the value of the conversation.properties() object or the default object. 

module.exports = {

Note: The code above defined a variable " _defaults"  that holds an object with the default values. You could also have the variable assignment defined as: var { variable, name = 'Jim Ben', age = 28, mail = '[email protected]' } = conversation.properties() || {}; 

With the above code, the following BotML configuration produces the following results:

discover destructuring assignment concept

Anything More To Know?

Yes. Lets assume you want to split the variable declaration and the value assignment (for whatever reason).

So you want to put it this way:

This doesn't work - and does not even allow you to import the custom component to the local skill container - because the destructuring code line is neither an assignment nor a valid expression.

So what you need to do, to make this work, is to wrap the destructuring directive in brackets: "(" and ")"

Notice the two changes :

  • The destructuring assignment is enclosed in brackets. 
  • The default values could not be read from the "_defaults" object as this is out of scope for the expression as it is now enclosed by brackets. As you can see in the code above, the default values are set directly in the destructuring definition. 

Related Content

MDN Webdocs - Destructuring assignment

TechExchange: How-to Build Card Layout Responses from Custom Components

TechExchange - Real World Insight into KeepTurn and Transition in Intelligent Bots

Custom Component Development with Oracle Bots Node.js SDK

TechExchange - Debugging Custom Components

Frank Nimphius

Master principal product manager.

Frank Nimphius is a Master Principal Product Manager at Oracle Corporation where he works on Oracle Digital Assistant and Health AI

Frank joined Oracle Product Management more than 20 years ago and since then worked on various Oracle products including Oracle Forms, Oracle JDeveloper, Oracle Application Development Framework (ADF) and the Mobile Application Framework (MAF) and Oracle Mobile Hub.

In his 20+ years at Oracle Frank enjoyed the many opportunities the job offered and became an author, an in-class and online-video trainer, a presenter at various international conferences, a collateral and training writer, a Java developer, as well as a product marketer and blogger.

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  1. Students 👹‍🎓 Vs Teacher đŸ‘©â€đŸ« ~ Assignment concept

  2. Teacher đŸ§‘â€đŸ« Vs Student🧑‍🎓 ~ Assignment concept 😂

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  4. Use Destructuring Assignment to Pass an Object as a Function's Parameters (ES6) freeCodeCamp

  5. Frontend Development Using React: Destructuring Assignment

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COMMENTS

  1. Destructuring Assignment in JavaScript

    Destructuring Assignment is a JavaScript expression that allows to unpack values from arrays, or properties from objects, into distinct variables data can be extracted from arrays, objects, nested objects and assigning to variables. In Destructuring Assignment on the left-hand side defined that which value should be unpacked from the sourced ...

  2. Destructuring assignment

    Destructuring with more elements than the source. In an array destructuring from an array of length N specified on the right-hand side of the assignment, if the number of variables specified on the left-hand side of the assignment is greater than N, only the first N variables are assigned values. The values of the remaining variables will be ...

  3. Destructuring assignment

    It's called "destructuring assignment," because it "destructurizes" by copying items into variables. However, the array itself is not modified. It's just a shorter way to write: // let [firstName, surname] = arr; let firstName = arr [0]; let surname = arr [1]; Ignore elements using commas.

  4. ES6 Destructuring Assignment Explained By Examples

    Fortunately, starting from ES6, you can use the destructing assignment as follows: console .log(x); // 70 console .log(y); // 80 console .log(z); // 90 Code language: JavaScript (javascript) The variables x, y and z will take the values of the first, second, and third elements of the returned array.

  5. How Destructuring Works in JavaScript

    Destructuring is a powerful JavaScript feature introduced in ES6 (ECMAScript 2015). It makes it easier to extract values from arrays or properties from objects and assign them to variables in a readable way. Let's delve into how destructuring works and explore various use cases with examples. You can get

  6. Understanding JavaScript's Destructuring Syntax Through Examples

    JavaScript has the destructuring assignment syntax to allow you to unpack objects and arrays into variables. I still see a lot of code where either the developer is not aware of this language feature or just didn't use it. The feature was added in ES6 and enables terser code without the loss of intent.

  7. JavaScript Destructuring Assignment

    JavaScript Destructuring. The destructuring assignment introduced in ES6 makes it easy to assign array values and object properties to distinct variables. For example, Before ES6: // assigning object attributes to variables const person = {. name: 'Sara', age: 25, gender: 'female'. }

  8. An Intro to JavaScript Destructuring Assignment

    without destructuring, each variable is assigned separately. This is not very efficient. Now let's look at a simple example of destructuring assignment. the assignment is done all in one line ...

  9. Destructuring assignment

    The ( ..) around the assignment statement is required syntax when using object literal destructuring assignment without a declaration. {a, b} = {a: 1, b: 2} is not valid stand-alone syntax, as the {a, b} on the left-hand side is considered a block and not an object literal. However, ({a, b} = {a: 1, b: 2}) is valid, as is var {a, b} = {a: 1, b: 2} NOTE: Your ( ..) expression needs to be ...

  10. Destructuring assignment

    Destructuring assignment. importance: 5. We have an object: let user = { name: "John", years: 30 }; Write the destructuring assignment that reads: name property into the variable name. years property into the variable age. isAdmin property into the variable isAdmin (false, if no such property)

  11. What is destructuring assignment and its uses?

    3. It is something like what you have can be extracted with the same variable name. The destructuring assignment is a JavaScript expression that makes it possible to unpack values from arrays or properties from objects into distinct variables. Let's get the month values from an array using destructuring assignment.

  12. JavaScript Destructuring [In-Depth Tutorial]

    Simple Examples to understand the concept. As stated earlier, JavaScript destructuring is a way to extract values from arrays, or properties from objects, and assign them to variables. It is a concise way to create variables from data stored in objects and arrays. ... The destructuring assignment for objects involves curly braces: let {a, b ...

  13. Mastering Destructuring in JavaScript: Unpacking the Power

    Destructuring assignment is a powerful feature in JavaScript that allows developers to extract values from arrays or properties from objects into distinct variables. This concept not only makes ...

  14. Efficient Coding with JavaScript Object Destructuring: A Practical Guide

    JavaScript Object Destructuring is a powerful feature that was introduced with ES6, simplifying the process of extracting data from objects and arrays. This technique enables developers to write cleaner and more efficient code, making it easier to read and maintain. In this article, we'll dive deep into the world of object destructuring ...

  15. Understanding Object Destructuring in JavaScript: A Beginner's Guide

    By using the destructuring assignment syntax, we can efficiently extract the elements we want from an array and assign them to new variables in a readable and concise manner. ... Destructuring is an interesting concept in JavaScript that allows values to be extracted from arrays or objects. Although it can be very simple at first, destructuring ...

  16. What is Object Destructuring?

    Array destructuring allows us to assign every value in an array to its variable. Since the introduction of the spread operator, it's quite simple to split up an array into values that are relevant for the user. Secondly, there is object destructuring. I find this feature way more powerful than array destructuring.

  17. Destructuring assignment in JavaScript

    Destructuring assignment syntax (Introduced in ES6) is a JavaScript expression that allows us to extract data from arrays, objects, and maps and set them into new, distinct variables. For example ...

  18. What is a Destructuring assignment and explain it in brief in

    The Destructuring assignment is the important technique introduced in ECMAScript 2015 (ES6) version of JavaScript that provides a shorthand syntax to extract or unpack array elements or properties of an object into distinct variables using a single line of code. In other words, this assignment helps us to segregate data of any iterable as well ...

  19. Discover JavaScript Destructuring: The Easy Way!

    Apply default values when destructuring arrays to handle undefined or missing elements. Discover an elegant technique for swapping variable values through destructuring assignment. By the end of this lesson, you'll have a comprehensive grasp of JavaScript destructuring. 🎓 Why Join: Real-Life Examples; Friendly Guidance; Learn at Your Pace

  20. JavaScript-classes-and-inheritance/interview.md at main

    Understand and able to use spread operator for Array concatenation Destructuring assignment; Be able to discover destructuring assignment concept; Understand variables and Function arguments destructuring assignment; String templates; Know how for..of loop works (optional) Advanced Functions. this scope; Reference Type & losing this

  21. Destructuring assignment: a reintroduction

    Hello, I will go through the destructuring assignment concept itself, then cover up the challenge afterwards:. Destructuring assignment: a reintroduction. The destructuring assignment syntax is a JavaScript expression that makes it possible to unpack values from arrays, or properties from objects, into distinct variables. "Come again? I don't get your MDN copy-paste explanation
"

  22. TechExchange Quick-Tip: The Benefits of Using JavaScript Destructuring

    ES 6, known as ECMA Script 2015 or JavaScript 6, introduced the concept of destructuring. Destructuring is a JavaScript expression syntax that reads values from arrays and objects and assigns them to variables. Custom components in Oracle Digital Assistant support JavaScript destructuring and custom component developers may use this syntax to assign component input parameter values to ...

  23. ESLint Must use destructuring state assignment

    Enforce consistent usage of destructuring assignment of props, state, and context (react/destructuring-assignment) More details are available here: destructuring-assignment.