`keys()` 返回一个新的 `Iterator` 对象。它包含按照顺序插入 `Map` 对象中每个元素的key值。

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

## 语法

    myMap.keys()

### 返回值

一个新的 `Map` iterator 对象.

## 例子

### 使用 `keys()`

    var myMap = new Map();
    myMap.set("0", "foo");
    myMap.set(1, "bar");
    myMap.set({}, "baz");

    var mapIter = myMap.keys();

    console.log(mapIter.next().value); // "0"
    console.log(mapIter.next().value); // 1
    console.log(mapIter.next().value); // Object

## 规范

规范 | 状态 | 备注
--- | --- | ---
ECMAScript 2015 (6th Edition, ECMA-262) Map.prototype.keys | Standard | Initial definition.
ECMAScript Latest Draft (ECMA-262) Map.prototype.keys | Draft |

## 浏览器兼容性

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
`keys` | Chrome Full support 38 | Edge Full support 12 | Firefox Full support 20 | IE No support No | Opera Full support 25 | Safari Full support 8 | WebView Android Full support 38 | Chrome Android Full support 38 | Edge Mobile Full support 12 | Firefox Android Full support 20 | Opera Android Full support 25 | Safari iOS Full support 8 | Samsung Internet Android Full support Yes | nodejs Full support 0.12

### Legend

Full support
  Full support
No support
  No support

## 参见

- `Map.prototype.entries()`
- `Map.prototype.values()`