javascript multiple variable assignment one line

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How to declare multiple Variables in JavaScript?

In this article, we will see how to declare multiple Variables in JavaScript. The variables can be declared using var , let , and const keywords. Variables are containers that store some value and they can be of any type.

These are the following ways to declare multiple variables:

Table of Content

Declaring Variables Individually

Declaring variables in a single line, using destructuring assignment.

In this case, we will declare each variable using the var, let, or const keywords.

Example: In this example, we are declaring three different variables.

You can declare multiple variables in a single line using the var, let, or const keyword followed by a comma-separated list of variable names.

Example: In this example, we are defining the three variables at once.

You can also use de-structuring assignments to declare multiple variables in one line and assign values to them.

Example: In this example, we are declaring three different variable by destructuring them at once.

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JavaScript declare multiple variables tutorial

by Nathan Sebhastian

Posted on May 02, 2021

Reading time: 2 minutes

The most common way to declare and initialize JavaScript variables is by writing each variable in its own line as follows:

But there are actually shorter ways to declare multiple variables using JavaScript. First, you can use only one variable keyword (var, let, or const) and declare the variable names and values separated by commas.

Take a look at the following example:

The declaration above just use one line, but it’s a bit harder to read than separated declarations. Furthermore, all the variables are declared using the same keyword let . You can’t use other variable keywords like const and var .

You can also make a multi-line declaration using comma-separated declaration as shown below:

Finally, you can also use destructuring assignment to declare and initialize multiple variables in one line as follows:

The destructuring assignment from the code above extracts the array elements and assigns them to the variables declared on the left side of the = assignment operator.

The code examples above are some tricks you can use to declare multiple variables in one line with JavaScript. Still, the most common way to declare variables is to declare them one by one, because it decouples the declaration into its own line:

The code above will be the easiest to change later as your project grows.

You can only use one variable keyword when using comma-separated declaration and destructuring assignment, so you can’t change the variables from const to let without changing them all.

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Assign Multiple Variables to the Same Value in JavaScript

By James L.

Sometimes you may need to assign the same value to multiple variables. In this article, I will show you exactly how to assign the same value to multiple variables using different methods.

Method 1: Using the equal sign (=) consecutively

You can set multiple variables to the same value in JavaScript by using the equal sign (=) consecutively between the variable names and assigning a single value at the end when declaring the variables.

For example:

The above code is equivalent to

You can also declare the variables first and assign the value later.

You can also use the ‘let’ or ‘const’ keyword instead of ‘var’ to create variables.

You can also create an undeclared variable without using any keywords.

If you want to assign different values to different variables, you can also do that using the syntax below.

We can also assign different values to different variables in the same line of code.

After assigning the same value to multiple variables, if we update any of the variables, it will not affect others.

In the example below, variables a, b, and c are assigned to 10 initially and then b is changed to 20.

As you can see from the above example, only the value of variable b is changed to 20. Variables a and c are not affected when we update the value of variable b because all variables a, b, and c are assigned with a primitive value.

Variables assigned with primitive values like a number, string, boolean, bigint, undefined, symbol, and null get replaced when a new value is assigned to the same variable because primitive values are immutable. i.e. the value itself cannot be altered but the variable can be replaced. Same is not the case for non-primitive values.

You need to be very careful when assigning the same non-primitive value like array, function, and objects to multiple variables because non-primitive values are mutable. i.e. the value itself can be altered. So the value itself will be changed instead of the variable getting replaced.

If you use the equal sign (=) consecutively to create multiple variables with the same non-primitive value. If you update the value of one variable, the value of all the variables will be updated too.

As you can see from the above example that if we update the value of variable a, the value of both variables will be updated. This happens because both variables a and b points to the same array object. And if we update the value of one variable the others get affected too.

So if you want to handle them separately then you need to assign them separately.

Method 2: Using the destructuring assignment syntax

Destructuring assignment syntax is a javascript expression that helps us to unpack values from arrays or objects into different variables.

We can also assign multiple values to the same value using destructuring assignment syntax combined with the fill function.

A real-life analogy

We can easily grasp the concept of a “variable” if we imagine it as a “box” for data, with a uniquely-named sticker on it.

For instance, the variable message can be imagined as a box labelled "message" with the value "Hello!" in it:

We can put any value in the box.

We can also change it as many times as we want:

When the value is changed, the old data is removed from the variable:

We can also declare two variables and copy data from one into the other.

A variable should be declared only once.

A repeated declaration of the same variable is an error:

So, we should declare a variable once and then refer to it without let .

It’s interesting to note that there exist so-called pure functional programming languages, such as Haskell , that forbid changing variable values.

In such languages, once the value is stored “in the box”, it’s there forever. If we need to store something else, the language forces us to create a new box (declare a new variable). We can’t reuse the old one.

Though it may seem a little odd at first sight, these languages are quite capable of serious development. More than that, there are areas like parallel computations where this limitation confers certain benefits.

Variable naming

There are two limitations on variable names in JavaScript:

• The name must contain only letters, digits, or the symbols $ and _ .
• The first character must not be a digit.

Examples of valid names:

When the name contains multiple words, camelCase is commonly used. That is: words go one after another, each word except first starting with a capital letter: myVeryLongName .

What’s interesting – the dollar sign '$' and the underscore '_' can also be used in names. They are regular symbols, just like letters, without any special meaning.

These names are valid:

Examples of incorrect variable names:

Variables named apple and APPLE are two different variables.

It is possible to use any language, including Cyrillic letters, Chinese logograms and so on, like this:

Technically, there is no error here. Such names are allowed, but there is an international convention to use English in variable names. Even if we’re writing a small script, it may have a long life ahead. People from other countries may need to read it sometime.

There is a list of reserved words , which cannot be used as variable names because they are used by the language itself.

For example: let , class , return , and function are reserved.

The code below gives a syntax error:

Normally, we need to define a variable before using it. But in the old times, it was technically possible to create a variable by a mere assignment of the value without using let . This still works now if we don’t put use strict in our scripts to maintain compatibility with old scripts.

This is a bad practice and would cause an error in strict mode:

To declare a constant (unchanging) variable, use const instead of let :

Variables declared using const are called “constants”. They cannot be reassigned. An attempt to do so would cause an error:

When a programmer is sure that a variable will never change, they can declare it with const to guarantee and communicate that fact to everyone.

Uppercase constants

There is a widespread practice to use constants as aliases for difficult-to-remember values that are known before execution.

Such constants are named using capital letters and underscores.

For instance, let’s make constants for colors in so-called “web” (hexadecimal) format:

• COLOR_ORANGE is much easier to remember than "#FF7F00" .
• It is much easier to mistype "#FF7F00" than COLOR_ORANGE .
• When reading the code, COLOR_ORANGE is much more meaningful than #FF7F00 .

When should we use capitals for a constant and when should we name it normally? Let’s make that clear.

Being a “constant” just means that a variable’s value never changes. But some constants are known before execution (like a hexadecimal value for red) and some constants are calculated in run-time, during the execution, but do not change after their initial assignment.

For instance:

The value of pageLoadTime is not known before the page load, so it’s named normally. But it’s still a constant because it doesn’t change after the assignment.

In other words, capital-named constants are only used as aliases for “hard-coded” values.

Name things right

Talking about variables, there’s one more extremely important thing.

A variable name should have a clean, obvious meaning, describing the data that it stores.

Variable naming is one of the most important and complex skills in programming. A glance at variable names can reveal which code was written by a beginner versus an experienced developer.

In a real project, most of the time is spent modifying and extending an existing code base rather than writing something completely separate from scratch. When we return to some code after doing something else for a while, it’s much easier to find information that is well-labelled. Or, in other words, when the variables have good names.

Please spend time thinking about the right name for a variable before declaring it. Doing so will repay you handsomely.

Some good-to-follow rules are:

• Use human-readable names like userName or shoppingCart .
• Stay away from abbreviations or short names like a , b , and c , unless you know what you’re doing.
• Make names maximally descriptive and concise. Examples of bad names are data and value . Such names say nothing. It’s only okay to use them if the context of the code makes it exceptionally obvious which data or value the variable is referencing.
• Agree on terms within your team and in your mind. If a site visitor is called a “user” then we should name related variables currentUser or newUser instead of currentVisitor or newManInTown .

Sounds simple? Indeed it is, but creating descriptive and concise variable names in practice is not. Go for it.

And the last note. There are some lazy programmers who, instead of declaring new variables, tend to reuse existing ones.

As a result, their variables are like boxes into which people throw different things without changing their stickers. What’s inside the box now? Who knows? We need to come closer and check.

Such programmers save a little bit on variable declaration but lose ten times more on debugging.

An extra variable is good, not evil.

Modern JavaScript minifiers and browsers optimize code well enough, so it won’t create performance issues. Using different variables for different values can even help the engine optimize your code.

We can declare variables to store data by using the var , let , or const keywords.

• let – is a modern variable declaration.
• var – is an old-school variable declaration. Normally we don’t use it at all, but we’ll cover subtle differences from let in the chapter The old "var" , just in case you need them.
• const – is like let , but the value of the variable can’t be changed.

Variables should be named in a way that allows us to easily understand what’s inside them.

Working with variables

• Declare two variables: admin and name .
• Assign the value "John" to name .
• Copy the value from name to admin .
• Show the value of admin using alert (must output “John”).

In the code below, each line corresponds to the item in the task list.

Giving the right name

• Create a variable with the name of our planet. How would you name such a variable?
• Create a variable to store the name of a current visitor to a website. How would you name that variable?

The variable for our planet

That’s simple:

Note, we could use a shorter name planet , but it might not be obvious what planet it refers to. It’s nice to be more verbose. At least until the variable isNotTooLong.

The name of the current visitor

Again, we could shorten that to userName if we know for sure that the user is current.

Modern editors and autocomplete make long variable names easy to write. Don’t save on them. A name with 3 words in it is fine.

And if your editor does not have proper autocompletion, get a new one .

Uppercase const?

Examine the following code:

Here we have a constant birthday for the date, and also the age constant.

The age is calculated from birthday using someCode() , which means a function call that we didn’t explain yet (we will soon!), but the details don’t matter here, the point is that age is calculated somehow based on the birthday .

Would it be right to use upper case for birthday ? For age ? Or even for both?

We generally use upper case for constants that are “hard-coded”. Or, in other words, when the value is known prior to execution and directly written into the code.

In this code, birthday is exactly like that. So we could use the upper case for it.

In contrast, age is evaluated in run-time. Today we have one age, a year after we’ll have another one. It is constant in a sense that it does not change through the code execution. But it is a bit “less of a constant” than birthday : it is calculated, so we should keep the lower case for it.

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How to Declare Multiple Variables in JavaScript

• JavaScript Howtos
• How to Declare Multiple Variables in …

Variables are containers in JavaScript that hold reusable data. They’re like cups filled with stuff that can be used repeatedly depending on how we want to use it.

Here are some JavaScript tips for declaring multiple variables.

Declare Multiple Variables in JavaScript

The most common method for declaring and initializing JavaScript variables is to write each variable on its line.

Example Code:

However, there are shorter ways to declare multiple variables in JavaScript. First, you can only use one variable keyword ( var , let , or const ) and declare variable names and values separated by commas.

The declaration above is only one line long, but it is more challenging to read than separated declarations. In addition, all variables are declared with the same keyword, let .

Other variable keywords, such as const and var, are not permitted. You can also use comma-separated declarations to create a multi-line declaration.

Finally, the de-structuring assignment can be used to reveal and preprocess multiple variables in a single line.

The array elements are extracted and assigned to the variables declared on the = operator’s left side in the code above.

The code examples above demonstrate how to declare multiple variables in a single line of JavaScript. Still, declaring variables one by one is the most common method because it separates the declaration into its line, like the following example below.

As your project grows, the code above will be the easiest to change.

When using comma-separated declaration and de-structuring assignment, you can only use one variable keyword, so you can’t change the variables from const to let without changing them all. In their own way, these variable types are distinct and help speed up code development.

However, it is recommended to use let whenever possible. You can use const whenever the variable’s value must remain constant.

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• How to Declare Multiple Variables in a Single Line in JavaScript

How to Declare Multiple Variables in One Line In JavaScript

In JavaScript, you can declare multiple variables in one line using the comma operator or the destructuring assignment syntax. This article explores both methods and provides detailed examples to illustrate their usage.

When writing JavaScript code, it’s important to optimize efficiency and readability. One way to achieve this is by declaring multiple variables in a single line of code. This not only saves space but also allows for concise and efficient coding practices. In this article, we will explore two methods to declare multiple variables in one line: using the comma operator and employing the destructuring assignment syntax.

Table of Contents

Using the comma operator.

The comma operator in JavaScript allows you to combine multiple expressions into a single expression. When used in variable declarations, it enables you to declare multiple variables in a single line. Here’s an example:

In this example, we declare three variables a , b , and c in one line, assigning them values of 1 , 2 , and 3 , respectively. This method is particularly useful when you want to declare and initialize multiple variables simultaneously.

You can also use the comma operator to declare variables without assigning them initial values:

In this case, x , y , and z are declared but remain undefined until assigned a value later in the code.

Exploring Destructuring Assignment

Destructuring assignment is another powerful feature in JavaScript that allows you to extract values from arrays or objects into distinct variables. It also enables you to declare multiple variables in one line while assigning them values from an array or an object. Let’s take a look at some examples:

Destructuring Arrays

In this example, we declare and assign values to variables a , b , and c using array destructuring. The values 1 , 2 , and 3 are extracted from the array and assigned to the respective variables.

You can also skip elements in the array by using commas:

In this case, the value 5 is skipped and not assigned to any variable.

Destructuring Objects

Similarly, you can use destructuring assignment with objects:

Here, we declare variables firstName and lastName , extracting their values from the corresponding properties of the object.

You can also provide default values in case the property is undefined:

In this example, if the property age is not present in the object, it defaults to 25 .

Declaring multiple variables in one line can greatly enhance the efficiency and readability of your JavaScript code. In this article, we explored two methods to achieve this: using the comma operator and leveraging destructuring assignment with arrays and objects. By using these techniques appropriately, you can write concise and optimized code.

Remember, when declaring multiple variables in one line, ensure that the code remains readable and maintainable. It’s always recommended to use descriptive variable names and follow best practices to enhance the overall quality of your code.

Now that you have a solid understanding of how to declare multiple variables in one line in JavaScript, go ahead and leverage this technique to streamline your coding practices!

Happy coding!

• MDN Web Docs: Comma Operator
• MDN Web Docs: Destructuring Assignment

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JavaScript multiple assignment

In JavaScript, you can assign multiple variables in the same line of code:

And you can also assign several variables together:

What just happened? Assignment is right associative (pairs from right to left), so you can think of the previous code as being the same as:

The right most pair is like an assignment when you forget to put the var keyword.

You can also think about var a = (b = 3) as:

Avoid creating global variables (window.a is a global variable). If you create global variables, you can create bugs when you use the same variable name.

What's the output?

What's the console output.

How to declare multiple variables in JavaScript self.__wrap_n=self.__wrap_n||(self.CSS&&CSS.supports("text-wrap","balance")?1:2);self.__wrap_b=(r,n,e)=>{e=e||document.querySelector(`[data-br="${r}"]`);let o=e.parentElement,l=u=>e.style.maxWidth=u+"px";e.style.maxWidth="";let s,i=o.clientWidth,p=o.clientHeight,a=i/2-.25,d=i+.5;if(i){for(l(a),a=Math.max(e.scrollWidth,a);a+1 {self.__wrap_b(0,+e.dataset.brr,e)})).observe(o)};self.__wrap_n!=1&&self.__wrap_b(":R16976:",1)

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JavaScript lets you declare multiple variables in a single statement, streamlining the process of setting up your variables. This guide dives into the syntax and strategies for declaring multiple variables efficiently in JavaScript.

Declaring multiple variables with one var keyword

The var keyword can be used to declare multiple variables at once, separated by commas. This method was commonly used in ES5 and earlier versions:

However, it's worth noting that var has function scope and is hoisted, which can lead to unexpected behaviors in certain situations.

Using let for block-scoped variables

ES6 introduced let , which allows for block-scoped variable declarations. Like var , you can declare multiple variables in one line:

Since let has block scope, it reduces the risk of errors related to variable hoisting and scope leakage.

Declaring with const for constants

When you need to declare variables whose values should not change, use const . Similar to let , you can declare multiple constants in a single line:

Remember that each constant must be initialized at the time of declaration, as their values cannot be reassigned later.

Grouping declarations and assignments

You can group variable declarations without initialization and then assign values later:

This can improve readability, especially when variable names are related or when initializing with values derived from complex expressions.

One-liner with destructuring assignment

Destructuring allows you to declare multiple variables by extracting values from arrays or objects:

For objects:

Destructuring can be especially handy for functions that return multiple values.

Default values with destructuring

When destructuring, you can also set default values for your variables in case the value extracted is undefined :

In the example above, j will default to 10 and k will be set to 21 .

Nested destructuring

For more complex data structures, nested destructuring can declare multiple variables at various levels of the structure:

This will declare n , o , and p with values 11 , 12 , and 13 respectively.

For loops and variable declarations

Within for loops, it's common to declare a loop variable, but you can declare additional variables as well:

Here, q and r are loop variables with different iteration logic.

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Temporal dead zone and let / const

It's important to remember that let and const declarations are subject to the Temporal Dead Zone (TDZ), meaning they cannot be accessed before declaration:

Tips for clean code

When declaring multiple variables, aim for clarity:

• Use one let or const per variable for easier debugging and readability.
• Group related declarations together.
• Initialize variables with values as close to the declaration as possible.

By following these practices, you ensure that your variable declarations enhance, rather than obfuscate, the readability and maintainability of your JavaScript code.

Additional contexts for declaring variables

Using variables in different scopes.

Discuss the nuances of variable scope:

var hoisting peculiarities

Explain the behavior of var regarding hoisting:

Advanced variable declaration patterns

Chained variable assignments.

Chain variable assignments carefully:

Variables in try-catch blocks

Handle try-catch with variable scopes:

Use in modern JavaScript frameworks

Demonstrate variable declarations in frameworks:

Additional good practices

Minimizing global variables.

Limit global variables as much as possible.

Naming conventions

Adopt clear naming conventions:

Performance considerations

Consider performance in declarations:

Debugging and variable declarations

Factor in the implications on debugging when declaring variables.

Cleaning up unused variables

Regularly remove unused variables to clean up your codebase.

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How to Declare Multiple Variables at Once in JavaScript

• #javascript

Table of Contents

Declaring multiple variables using commas.

Variables are a fundamental part of any programming language, especially JavaScript .

Declaring variables is how you define a variable in JavaScript that you can optionally give a value to.

In this post, we'll look at how to declare multiple variables in JavaScript.

The most common way to declare multiple variables in JavaScript is to use commas to separate the variable names.

This is the same as declaring each variable individually.

You can also initialize them with values:

You can improve readability by declaring each variable on a separate line:

Another way you can define multiple variables is by using an array:

This can be useful especially when you don't control the values of the array and want to define variables for each value.

Keep in mind that if the value of the variable is not going to change, you should use const instead of let .

In this post, we looked at how to declare multiple variables in JavaScript.

You can declare multiple variables using commas or by using an array, whichever makes the most sense for you.

Thanks for reading!

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Declare multiple variables in single line JavaScript

The most common way to declare a javascript variable is by writing each variable in a new line, for example.

You can view the above variable are declared in the new line, but you can write the above-declared variable in a single line. for example,

The declaration above is in one line, we have declared are variable using the same keyword let.

Declare multiple variables in single line using destructuring assignment

Even you can declare a variable by using the let or var keyword one time and declaring multiple variables in a new inline

You can choose any keyword var, const, or let while declaring variable

create multiple variables in one line js

Answered on: Saturday 02 December, 2023 / Duration: 13 min read

Programming Language: JavaScript , Popularity : 3/10

Solution 1:

### In-depth explanation for creating multiple variables in one line in JavaScript

In JavaScript, you can create multiple variables in one line by using the following syntax:

This syntax creates three variables, var1 , var2 , and var3 , and assigns the values 1 , 2 , and 3 to them, respectively.

You can also use the following syntax to create multiple variables in one line:

Example code:

### Additional resources

* [MDN: Multiline variable declarations](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const#Multiline_variable_declarations) * [W3Schools: JavaScript: Multiline variable declaration](https://www.w3schools.com/js/js_variables_multiple.asp)

Solution 2:

In JavaScript, you can create multiple variables in one line using the comma operator ( , ). The comma operator separates expressions, allowing you to define multiple variables in a single statement.

Here's an example:

This statement declares three variables: x with the value 5 , y with the value 10 , and z with the value 'hello' (a string).

You can also use the comma operator to assign values to existing variables in a single statement:

In this example, we first declare a variable x with the value 5 . Then, on the same line, we use the comma operator to assign a new value to x ( 10 ), and also declare a new variable z with the value 'hello' .

It's important to note that when using the comma operator, the right-most expression is the one that gets evaluated last. So in the second example above, z will be assigned the value 'hello' before x is reassigned to 10 .

Here's another example of creating multiple variables in one line using destructuring:

In this example, we are using array destructuring to create three variables a , b , and c and assigning them the values from an array [1, 2, 3] .

It's also worth noting that you can mix and match different ways of declaring variables in the same statement. For example:

In this example, we declare two variables x and y traditionally, and then use object destructuring to create a new variable z and assign it the value 'hello' (a string) while also creating a new object with the keys a and b and values 'hello' and 'world' respectively.

It's important to keep in mind that although it's possible to create multiple variables in one line, it's generally considered better practice to avoid doing so, especially in complex operations, as it can make the code harder to read and understand.

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Multiple variable assignment with Javascript

About a month ago I posted how it is possible to assign multiple variables with the same value in PHP and have since learned that this is also possible to do with Javascript. This can be useful if initializing multiple variables with the same initial value or if needing to make multiple copies of a value and then manipulate each separately.

Assigning multiple variables

Using the same set sort of examples as in the PHP post, but this time with Javascript, multiple variables can be assigned by using = multiple times on the same line of code like so:

The above is a more compact equivilent of this:

Here’s an example where all three variables are assigned initially with the string "AAA" and then the values of each are written out to the current page using document.write:

The resulting output on the page would look like this:

Any subsequent updates to any of the variables will not affect the other assigned variables. In the next example a, b and c are again initialised with "AAA" and then b is changed to "BBB".

The output from this example would be:

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Destructuring assignment

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 uses it on the left-hand side of the assignment instead. It defines which values to unpack from the sourced variable.

Similarly, you can destructure objects on the left-hand side of the assignment.

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

For features specific to array or object destructuring, refer to the individual examples below.

Binding and assignment

For both object and array destructuring, there are two kinds of destructuring patterns: binding pattern and assignment pattern , with slightly different syntaxes.

In binding patterns, the pattern starts with a declaration keyword ( var , let , or const ). Then, each individual property must either be bound to a variable or further destructured.

All variables share the same declaration, so if you want some variables to be re-assignable but others to be read-only, you may have to destructure twice — once with let , once with const .

In many other syntaxes where the language binds a variable for you, you can use a binding destructuring pattern. These include:

• The looping variable of for...in for...of , and for await...of loops;
• Function parameters;
• The catch binding variable.

In assignment patterns, the pattern does not start with a keyword. Each destructured property is assigned to a target of assignment — which may either be declared beforehand with var or let , or is a property of another object — in general, anything that can appear on the left-hand side of an assignment expression.

Note: The parentheses ( ... ) around the assignment statement are required 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 according to the rules of expression statements . However, ({ a, b } = { a: 1, b: 2 }) is valid, as is const { a, b } = { a: 1, b: 2 } .

If your coding style does not include trailing semicolons, the ( ... ) expression needs to be preceded by a semicolon, or it may be used to execute a function on the previous line.

Note that the equivalent binding pattern of the code above is not valid syntax:

You can only use assignment patterns as the left-hand side of the assignment operator. You cannot use them with compound assignment operators such as += or *= .

Default value

Each destructured property can have a default value . The default value is used when the property is not present, or has value undefined . It is not used if the property has value null .

The default value can be any expression. It will only be evaluated when necessary.

Rest property

You can end a destructuring pattern with a rest property ...rest . This pattern will store all remaining properties of the object or array into a new object or array.

The rest property must be the last in the pattern, and must not have a trailing comma.

Array destructuring

Basic variable 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 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:

Using a binding pattern as the rest property

The rest property of array destructuring assignment can be another array or object binding pattern. The inner destructuring destructures from the array created after collecting the rest elements, so you cannot access any properties present on the original iterable in this way.

These binding patterns can even be nested, as long as each rest property is the last in the list.

On the other hand, object destructuring can only have an identifier as the rest property.

Unpacking values from a regular expression match

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.

Using array destructuring on any iterable

Array destructuring calls the iterable protocol of the right-hand side. Therefore, any iterable, not necessarily arrays, can be destructured.

Non-iterables cannot be destructured as arrays.

Iterables are only iterated until all bindings are assigned.

The rest binding is eagerly evaluated and creates a new array, instead of using the old iterable.

Object destructuring

Basic assignment, 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.

Here, for example, const { p: foo } = o takes from the object o the property named p and assigns it to a local variable named foo .

Assigning to new variable names and providing default values

A property can be both

• Unpacked from an object and assigned to a variable with a different name.
• Assigned a default value in case the unpacked value is undefined .

Unpacking properties from objects passed as a function parameter

Objects passed into function parameters can also be unpacked into variables, which may then be accessed within the function body. As for object assignment, the destructuring syntax allows for the new variable to have the same name or a different name than the original property, and to assign default values for the case when the original object does not define the property.

Consider this object, which contains information about a user.

Here we show how to unpack a property of the passed object into a variable with the same name. The parameter value { id } indicates that the id property of the object passed to the function should be unpacked into a variable with the same name, which can then be used within the function.

You can define the name of the unpacked variable. Here we unpack the property named displayName , and rename it to dname for use within the function body.

Nested objects can also be unpacked. The example below shows the property fullname.firstName being unpacked into a variable called name .

Setting a function parameter's default value

Default values can be specified using = , and will be used as variable values if a specified property does not exist in the passed object.

Below we show a function where the default size is 'big' , default co-ordinates are x: 0, y: 0 and default radius is 25.

In the function signature for drawChart above, the destructured left-hand side has a default value of an empty object = {} .

You could have also written the function without that default. However, if you leave out that default value, the function will look for at least one argument to be supplied when invoked, whereas in its current form, you can call drawChart() without supplying any parameters. Otherwise, you need to at least supply an empty object literal.

For more information, see Default parameters > Destructured parameter with default value assignment .

Nested object and array destructuring

For of iteration and destructuring, computed object property names and destructuring.

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

Invalid JavaScript identifier as a property name

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

Destructuring primitive values

Object destructuring is almost equivalent to property accessing . This means if you try to destruct a primitive value, the value will get wrapped into the corresponding wrapper object and the property is accessed on the wrapper object.

Same as accessing properties, destructuring null or undefined throws a TypeError .

This happens even when the pattern is empty.

Combined array and object destructuring

Array and object destructuring can be combined. Say you want the third element in the array props below, and then you want the name property in the object, you can do the following:

The prototype chain is looked up when the object is deconstructed

When deconstructing an object, if a property is not accessed in itself, it will continue to look up along the prototype chain.

Specifications

Browser compatibility.

BCD tables only load in the browser with JavaScript enabled. Enable JavaScript to view data.

• Assignment operators
• ES6 in Depth: Destructuring on hacks.mozilla.org (2015)