加法赋值(+=)

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

加法赋值运算符(+=)将右操作数的值添加到变量,并将结果分配给该变量。两个操作数的类型决定了加法赋值运算符的行为,可能为加法或拼接。

尝试一下

let a = 2;
let b = "hello";

console.log((a += 3)); // Addition
// Expected output: 5

console.log((b += " world")); // Concatenation
// Expected output: "hello world"

语法

js
x += y // x = x + y

示例

使用加法赋值

js
let baz = true;

// Boolean + Number -> 加法
baz += 1; // 2

// Number + Boolean -> 加法
baz += false; // 2
js
let foo = "foo";

// String + Boolean -> 拼接
foo += false; // "foofalse"

// String + String -> 拼接
foo += "bar"; // "foofalsebar"
js
let bar = 5;

// Number + Number -> 加法
bar += 2; // 7

// Number + String -> 拼接
bar += "foo"; // "7foo"

规范

Specification
ECMAScript® 2025 Language Specification
# sec-assignment-operators

浏览器兼容性

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desktopmobileserver
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Deno
Node.js
Addition assignment (x += y)

Legend

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Full support
Full support

参见