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• 句法
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

has() method returns a boolean indicating whether an element with the specified key exists in the WeakMap object or not.

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.

句法

wm.has(key);
					

参数

key

Required. The key of the element to test for presence in the WeakMap 对象。

返回值

布尔

返回 true if an element with the specified key exists in the WeakMap object; otherwise false .

范例

使用 has 方法

var wm = new WeakMap();
wm.set(window, 'foo');
wm.has(window); // returns true
wm.has('baz');  // returns false
					

规范

规范
ECMAScript (ECMA-262) The definition of 'WeakMap.prototype.has' in that specification.

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. 更新 GitHub 上的兼容性数据

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
has	Chrome 36	Edge 12	Firefox 6 6 Prior to Firefox 38, this method threw a TypeError when the key parameter was not an object. This has been fixed in version 38 and later to return false as per the ES2015 standard.	IE 11	Opera 23	Safari 8	WebView Android 37	Chrome Android 36	Firefox Android 6 6 Prior to Firefox 38, this method threw a TypeError when the key parameter was not an object. This has been fixed in version 38 and later to return false as per the ES2015 standard.	Opera Android 24	Safari iOS 8	Samsung Internet Android 3.0	nodejs 0.12 0.12 0.10 Disabled Disabled From version 0.10: this feature is behind the --harmony runtime flag.

图例

完整支持

完整支持

见实现注意事项。

用户必须明确启用此特征。

用户必须明确启用此特征。

另请参阅

• WeakMap
• WeakMap.prototype.set()
• WeakMap.prototype.get()

元数据

• 最后修改： 2020 年 1 月 22 日

相关话题

1. 标准内置对象
2. WeakMap
3. 方法
   1. WeakMap.prototype.clear()
   2. WeakMap.prototype.delete()
   3. WeakMap.prototype.get()
   4. WeakMap.prototype.has()
   5. WeakMap.prototype.set()
4. 继承：
5. Function
6. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
7. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
8. Object
9. 特性
   1. Object.prototype.__proto__
   2. Object.prototype.constructor
10. 方法
    1. Object.prototype.__defineGetter__()
    2. Object.prototype.__defineSetter__()
    3. Object.prototype.__lookupGetter__()
    4. Object.prototype.__lookupSetter__()
    5. Object.prototype.hasOwnProperty()
    6. Object.prototype.isPrototypeOf()
    7. Object.prototype.propertyIsEnumerable()
    8. Object.prototype.toLocaleString()
    9. Object.prototype.toSource()
    10. Object.prototype.toString()
    11. Object.prototype.valueOf()
    12. Object.setPrototypeOf()