加法赋值 (+=)

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加法赋值操作符 (+=) 将右操作数的值添加到变量,并将结果分配给该变量。两个操作数的类型确定加法赋值运算符的行为。加法或串联是可能的。

Syntax

Operator: x += y
Meaning:  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

Specification
ECMAScript (ECMA-262)
Assignment operators

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
Addition assignment (x += y)Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 3Opera Full support 3Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support 0.1.100

Legend

Full support  
Full support

See also