在此页

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

forEach() method executes a provided function once for each value in the Set object, in insertion order.

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

mySet.forEach(callback[, thisArg])
					

参数

callback

Function to execute for each element, taking three arguments:

currentValue , currentKey

The current element being processed in the Set . As there are no keys in Set , the value is passed for both arguments.

set

Set object which forEach() was called upon.

thisArg

Value to use as this when executing callback .

返回值

undefined .

描述

forEach() method executes the provided callback once for each value which actually exists in the Set object. It is not invoked for values which have been deleted. However, it is executed for values which are present but have the value undefined .

callback is invoked with three arguments :

• the element value
• the element key
• the Set object being traversed

There are no keys in Set objects, however, so the first two arguments are both 值 contained in the Set . This is to make it consistent with other forEach() methods for Map and Array .

若 thisArg parameter is provided to forEach() , it will be passed to callback when invoked, for use as its this value.  Otherwise, the value undefined will be passed for use as its this value.  The this value ultimately observable by callback is determined according to the usual rules for determining the this seen by a function .

Each value is visited once, except in the case when it was deleted and re-added before forEach() has finished. callback is not invoked for values deleted before being visited. New values added before forEach() has finished will be visited.

forEach() executes the callback function once for each element in the Set object; it does not return a value.

范例

Logging the contents of a Set object

The following code logs a line for each element in a Set 对象：

function logSetElements(value1, value2, set) {
    console.log('s[' + value1 + '] = ' + value2);
}
new Set(['foo', 'bar', undefined]).forEach(logSetElements);
// logs:
// "s[foo] = foo"
// "s[bar] = bar"
// "s[undefined] = undefined"
					

规范

规范
ECMAScript (ECMA-262) The definition of 'Set.prototype.forEach' 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
forEach	Chrome 38	Edge 12	Firefox 25	IE 11	Opera 25	Safari 8	WebView Android 38	Chrome Android 38	Firefox Android 25	Opera Android 25	Safari iOS 8	Samsung Internet Android 3.0	nodejs 0.12

图例

完整支持

完整支持

另请参阅

• Array.prototype.forEach()
• Map.prototype.forEach()

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. Set
3. 特性
   1. Set.prototype.size
   2. get Set[@@species]
4. 方法
   1. Set.prototype.add()
   2. Set.prototype.clear()
   3. Set.prototype.delete()
   4. Set.prototype.entries()
   5. Set.prototype.forEach()
   6. Set.prototype.has()
   7. Set.prototype.values()
   8. Set.prototype[@@iterator]()
5. 继承：
6. Function
7. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
8. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
9. Object
10. 特性
    1. Object.prototype.__proto__
    2. Object.prototype.constructor
11. 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()