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 |
