当尝试设置属性时，`set`语法将对象属性绑定到要调用的函数。

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## 语法

    {set prop(val) { . . . }}
    {set [expression](val) { . . . }}

### 参数

`prop`
  要绑定到给定函数的属性名。

`val`
  用于保存尝试分配给`prop`的值的变量的一个别名。
表达式
  从 ECMAScript 2015 开始，还可以使用一个计算属性名的表达式绑定到给定的函数。

## 描述

在 javascript 中，如果试着改变一个属性的值，那么对应的 setter 将被执行。setter 经常和 getter 连用以创建一个伪属性。不可能在具有真实值的属性上同时拥有一个 setter 器。

使用 set 语法时请注意：

- 它的标识符可以是数字或字符串；
- 它必须有一个明确的参数 （详见 Incompatible ES5 change: literal getter and setter functions must now have exactly zero or one arguments）；
- 在对象字面量中，不能为一个已有真实值的变量使用 set ，也不能为一个属性设置多个 set。
  ( `{ set x(v) { }, set x(v) { } }` 和 `{ x: ..., set x(v) { } }` 是不允许的 )

setter 可以用`delete`操作来移除。

## 示例

### 在对象初始化时定义 setter

这将定义一个对象 language 的伪属性`current`，当分配一个值时，将使用该值更新`log`：

    var language = {
      set current(name) {
        this.log.push(name);
      },
      log: []
    }

    language.current = 'EN';
    console.log(language.log); // ['EN']

    language.current = 'FA';
    console.log(language.log); // ['EN', 'FA']

请注意，`current`属性是未定义的，访问它时将会返回 `undefined`。

### 用 `delete` 操作符移除一个 setter

我们可以使用`delete`操作符移除 setter。

    delete o.current;

### 使用 `defineProperty` 为当前对象定义 setter

我们可以随时使用 `Object.defineProperty()` 给一个已经存在的对象添加一个 setter。

    var o = { a:0 };

    Object.defineProperty(o, "b", { set: function (x) { this.a = x / 2; } });

    o.b = 10; // Runs the setter, which assigns 10 / 2 (5) to the 'a' property
    console.log(o.a) // 5

### 使用计算属性名

    var expr = "foo";

    var obj = {
      baz: "bar",
      set [expr](v) { this.baz = v; }
    };

    console.log(obj.baz); // "bar"
    obj.foo = "baz";      // run the setter
    console.log(obj.baz); // "baz"

## 规范

Specification | Status | Comment
--- | --- | ---
ECMAScript 5.1 (ECMA-262) Object Initializer | Standard | Initial definition.
ECMAScript 2015 (6th Edition, ECMA-262) Method definitions | Standard | Added computed property names.
ECMAScript Latest Draft (ECMA-262) Method definitions | Draft |

## 浏览器兼容

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Update compatibility data on GitHub

| Desktop | Mobile | Server
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | Android webview | Chrome for Android | Edge Mobile | Firefox for Android | Opera for Android | Safari on iOS | Samsung Internet | Node.js
`set` | Chrome Full support 1 | Edge Full support Yes | Firefox Full support 2 | IE Full support 9 | Opera Full support 9.5 | Safari Full support 3 | WebView Android Full support 1 | Chrome Android Full support 18 | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes
Computed property names | Chrome Full support 46 | Edge Full support Yes | Firefox Full support 34 | IE No support No | Opera Full support 47 | Safari No support No | WebView Android Full support 46 | Chrome Android Full support 46 | Edge Mobile Full support Yes | Firefox Android Full support 34 | Opera Android Full support Yes | Safari iOS No support No | Samsung Internet Android Full support 5.0 | nodejs Full support Yes

### Legend

Full support
  Full support
No support
  No support

## 相关链接

- getter
- `delete`
- `Object.defineProperty()`
- `__defineGetter__`
- `__defineSetter__`
- Defining Getters and Setters in JavaScript Guide