W3cubDocs

/JavaScript

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.

Syntax

x += y // x = x + y

Examples

Using addition assignment

// 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"

Specifications

Browser compatibility

Desktop Mobile Server
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet Deno Node.js
Addition_assignment
1
12
1
3
3
1
1
18
4
10.1
1
1.0
1.0
0.10.0

See also

© 2005–2021 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Addition_assignment