Assignment Definition Programming

Variable Assignment

The '=' symbol is the assignment operator. Warning, while the assignment operator looks like the traditional mathematical equals sign, this is NOT the case. The equals operator is '=='

Design Pattern

To evaluate an assignment statement:

  1. Evaluate the "right side" of the expression (to the right of the equal sign).
  2. Once everything is figured out, place the computed value into the variables bucket.

More info

We've already seen many examples of assignment. Assignment means: "storing a value (of a particular type) under a variable name". Think of each assignment as copying the value of the righthand side of the expression into a "bucket" associated with the left hand side name!

Read this as, the variable called "name" is "assigned" the value computed by the expression to the right of the assignment operator ('=');

Now that you have seen some variables being assigned, tell me what the following code means?

The answer to above questions: the assignment means that lkjasdlfjlskdfjlksjdflkj is a variable (a really badly named one), but a variable none-the-less. jlkajdsf and lkjsdflkjsdf must also be variables. The sum of the two numbers held in jlkajdsf and lkjsdflkjsdf is stored in the variable lkjasdlfjlskdfjlksjdflkj.


Examples of builtin Data and Variables (and Constants)

For more info, use the "help" command: (e.g., help realmin);


Examples of using Data and Variable

PATTERN TO MEMORIZE

ASSIGNMENT PATTERN

The assignment pattern creates a new variable, if this is the first time we have seen the "name", or, updates the variable to a new value!

Read the following code in English as: First, compute the value of the thing to the right of the assignment operator (the =). then store the computed value under the given name, destroying anything that was there before.

Or more concisely: assign the variable "name" the value computed by "right_hand_expression"


Back to Topics List

An assignment operator assigns a value to its left operand based on the value of its right operand.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

Overview

The basic assignment operator is equal (), which assigns the value of its right operand to its left operand. That is, assigns the value of to . The other assignment operators are usually shorthand for standard operations, as shown in the following definitions and examples.

Assignment

Simple assignment operator which assigns a value to a variable. The assignment operation evaluates to the assigned value. Chaining the assignment operator is possible in order to assign a single value to multiple variables. See the example.

Syntax

Operator: x = y

Examples

// Assuming the following variables // x = 5 // y = 10 // z = 25 x = y // x is 10 x = y = z // x, y and z are all 25

Addition assignment

The addition assignment operator adds the value of the right operand to a variable and assigns the result to the variable. The types of the two operands determine the behavior of the addition assignment operator. Addition or concatenation is possible. See the addition operator for more details.

Syntax

Operator: x += y Meaning: x = x + y

Examples

// Assuming the following variables // foo = 'foo' // bar = 5 // baz = true // Number + Number -> addition bar += 2 // 7 // Boolean + Number -> addition baz += 1 // 2 // Boolean + Boolean -> addition baz += false // 1 // Number + String -> concatenation bar += 'foo' // "5foo" // String + Boolean -> concatenation foo += false // "foofalse" // String + String -> concatenation foo += 'bar' // "foobar"

Subtraction assignment

The subtraction assignment operator subtracts the value of the right operand from a variable and assigns the result to the variable. See the subtraction operator for more details.

Syntax

Operator: x -= y Meaning: x = x - y

Examples

// Assuming the following variable // bar = 5 bar -= 2 // 3 bar -= 'foo' // NaN

Multiplication assignment

The multiplication assignment operator multiplies a variable by the value of the right operand and assigns the result to the variable. See the multiplication operator for more details.

Syntax

Operator: x *= y Meaning: x = x * y

Examples

// Assuming the following variable // bar = 5 bar *= 2 // 10 bar *= 'foo' // NaN

Division assignment

The division assignment operator divides a variable by the value of the right operand and assigns the result to the variable. See the division operator for more details.

Syntax

Operator: x /= y Meaning: x = x / y

Examples

// Assuming the following variable // bar = 5 bar /= 2 // 2.5 bar /= 'foo' // NaN bar /= 0 // Infinity

Remainder assignment

The remainder assignment operator divides a variable by the value of the right operand and assigns the remainder to the variable. See the remainder operator for more details.

Syntax

Operator: x %= y Meaning: x = x % y

Examples

// Assuming the following variable // bar = 5 bar %= 2 // 1 bar %= 'foo' // NaN bar %= 0 // NaN

Exponentiation assignment

This is an experimental technology, part of the ECMAScript 2016 (ES7) proposal.
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future version of browsers as the spec changes.

The exponentiation assignment operator evaluates to the result of raising first operand to the power second operand. See the exponentiation operator for more details.

Syntax

Operator: x **= y Meaning: x = x ** y

Examples

// Assuming the following variable // bar = 5 bar **= 2 // 25 bar **= 'foo' // NaN

Left shift assignment

The left shift assignment operator moves the specified amount of bits to the left and assigns the result to the variable. See the left shift operator for more details.

Syntax

Operator: x <<= y Meaning: x = x << y

Examples

var bar = 5; // (00000000000000000000000000000101) bar <<= 2; // 20 (00000000000000000000000000010100)

Right shift assignment

The right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the right shift operator for more details.

Syntax

Operator: x >>= y Meaning: x = x >> y

Examples

var bar = 5; // (00000000000000000000000000000101) bar >>= 2; // 1 (00000000000000000000000000000001) var bar -5; // (-00000000000000000000000000000101) bar >>= 2; // -2 (-00000000000000000000000000000010)

Unsigned right shift assignment

The unsigned right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the unsigned right shift operator for more details.

Syntax

Operator: x >>>= y Meaning: x = x >>> y

Examples

var bar = 5; // (00000000000000000000000000000101) bar >>>= 2; // 1 (00000000000000000000000000000001) var bar = -5; // (-00000000000000000000000000000101) bar >>>= 2; // 1073741822 (00111111111111111111111111111110)

Bitwise AND assignment

The bitwise AND assignment operator uses the binary representation of both operands, does a bitwise AND operation on them and assigns the result to the variable. See the bitwise AND operator for more details.

Syntax

Operator: x &= y Meaning: x = x & y

Example

var bar = 5; // 5: 00000000000000000000000000000101 // 2: 00000000000000000000000000000010 bar &= 2; // 0

Bitwise XOR assignment

The bitwise XOR assignment operator uses the binary representation of both operands, does a bitwise XOR operation on them and assigns the result to the variable. See the bitwise XOR operator for more details.

Syntax

Operator: x ^= y Meaning: x = x ^ y

Example

var bar = 5; bar ^= 2; // 7 // 5: 00000000000000000000000000000101 // 2: 00000000000000000000000000000010 // ----------------------------------- // 7: 00000000000000000000000000000111

Bitwise OR assignment

The bitwise OR assignment operator uses the binary representation of both operands, does a bitwise OR operation on them and assigns the result to the variable. See the bitwise OR operator for more details.

Syntax

Operator: x |= y Meaning: x = x | y

Example

var bar = 5; bar |= 2; // 7 // 5: 00000000000000000000000000000101 // 2: 00000000000000000000000000000010 // ----------------------------------- // 7: 00000000000000000000000000000111

Examples

Left operand with another assignment operator

In unusual situations, the assignment operator (e.g.) is not identical to the meaning expression (here ). When the left operand of an assignment operator itself contains an assignment operator, the left operand is evaluated only once. For example:

a[i++] += 5 // i is evaluated only once a[i++] = a[i++] + 5 // i is evaluated twice

Specifications

Browser compatibility

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung InternetNode.js
Addition assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes
Bitwise AND assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes
Bitwise OR assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes
Bitwise XOR assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes
Division assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes
Exponentiation assignment ()Full support 52 ? Full support 52No support NoFull support Yes ? Full support 51Full support 52 ? Full support 52Full support Yes ? ? Full support Yes
Left shift assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes
Multiplication assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes
Remainder assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes
Right shift assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes
Assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes
Subtraction assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes
Unsigned right shift assignment ()Full support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support YesFull support Yes ? Full support Yes

Legend

Full support
Full support
No support
No support
Compatibility unknown
Compatibility unknown

See also

Document Tags and Contributors

 Contributors to this page:wbamberg, stephaniehobson, fscholz, jameshkramer, nmve, kdex, torazaburo, samuele-artuso, io-ma, Sebastianz, JDurston, phylasnier, Havvy, Delapouite, Meghraj, Sheppy, trevorh, ethertank, Potappo, Mgjbot, Marcoos, Dria

 Last updated by:wbamberg,

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