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® 2026 Language Specification # sec-assignment-operators |