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• 句法
• 描述
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

静态 Reflect .has() method works like the in operator as a function.

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

Reflect.has(target, propertyKey)
					

参数

target

The target object in which to look for the property.

propertyKey

The name of the property to check.

返回值

A 布尔 indicating whether or not the target has the property.

异常

A TypeError , if target is not an Object .

描述

Reflect.has method allows you to check if a property is in an object. It works like the in operator as a function.

范例

使用 Reflect.has()

Reflect.has({x: 0}, 'x')  // true
Reflect.has({x: 0}, 'y')  // false
// returns true for properties in the prototype chain
Reflect.has({x: 0}, 'toString')
// Proxy with .has() handler method
obj = new Proxy({}, {
  has(t, k) { return k.startsWith('door')  }
});
Reflect.has(obj, 'doorbell')  // true
Reflect.has(obj, 'dormitory')  // false
					

Reflect.has 返回 true for any inherited properties, like the in operator :

const a = {foo: 123}
const b = {__proto__: a}
const c = {__proto__: b}
// The prototype chain is: c -> b -> a
Reflect.has(c, 'foo') // true
					

规范

规范
ECMAScript (ECMA-262) The definition of 'Reflect.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 49	Edge 12	Firefox 42	IE No	Opera 36	Safari 10	WebView Android 49	Chrome Android 49	Firefox Android 42	Opera Android 36	Safari iOS 10	Samsung Internet Android 5.0	nodejs 6.0.0

图例

完整支持

完整支持

不支持

不支持

另请参阅

• Reflect
• in operator

元数据

• 最后修改： Jan 15, 2020

相关话题

1. 标准内置对象
2. Reflect
3. 方法
   1. Reflect.apply()
   2. Reflect.construct()
   3. Reflect.defineProperty()
   4. Reflect.deleteProperty()
   5. Reflect.get()
   6. Reflect.getOwnPropertyDescriptor()
   7. Reflect.getPrototypeOf()
   8. Reflect.has()
   9. Reflect.isExtensible()
   10. Reflect.ownKeys()
   11. Reflect.preventExtensions()
   12. Reflect.set()
   13. Reflect.setPrototypeOf()
4. 继承：
5. Object
6. 特性
   1. Object.prototype.__proto__
   2. Object.prototype.constructor
7. 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()