# Assignment operators

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

## Overview

The basic assignment operator is equal (`=`

), which assigns the value of its right operand to its left operand. That is, `x = y`

assigns the value of `y`

to `x`

. The other assignment operators are usually shorthand for standard operations, as shown in the following definitions and examples.

Name | Shorthand operator | Meaning |
---|---|---|

Assignment | `x = y` |
`x = y` |

Addition assignment | `x += y` |
`x = x + y` |

Subtraction assignment | `x -= y` |
`x = x - y` |

Multiplication assignment | `x *= y` |
`x = x * y` |

Division assignment | `x /= y` |
`x = x / y` |

Remainder assignment | `x %= y` |
`x = x % y` |

Exponentiation assignment | `x **= y` |
`x = x ** y` |

Left shift assignment | `x <<= y` |
`x = x << y` |

Right shift assignment | `x >>= y` |
`x = x >> y` |

Unsigned right shift assignment | `x >>>= y` |
`x = x >>> y` |

Bitwise AND assignment | `x &= y` |
`x = x & y` |

Bitwise XOR assignment | `x ^= y` |
`x = x ^ y` |

Bitwise OR assignment | `x |= y` |
`x = x | y` |

## 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.` x += y`

) is not identical to the meaning expression (here `x = x + y`

). When the left operand of an assignment operator itself contains an assignment operator, the left operand is evaluated only once. For example:

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

## Specifications

## Browser compatibility

Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|

Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |

Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|

Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |

## See also

## License

© 2016 Mozilla Contributors

Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

https://developer.mozilla.org/en-us/docs/web/javascript/reference/operators/assignment_operators