Set | JavaScript

在此页

描述
构造函数
静态特性
实例特性
实例方法
范例
规范
浏览器兼容性
另请参阅
相关话题

Set object lets you store unique values of any type, whether 原语值 or object references.

描述

Set objects are collections of values. You can iterate through the elements of a set in insertion order. A value in the Set may only occur once ; it is unique in the Set 's collection.

Value equality

Because each value in the Set has to be unique, the value equality will be checked. In an earlier version of ECMAScript specification, this was not based on the same algorithm as the one used in the === operator. Specifically, for Set s, +0 (which is strictly equal to -0 ) and -0 were different values. However, this was changed in the ECMAScript 2015 specification. See "Key equality for -0 and 0" 在 browser compatibility table for details.

NaN and undefined can also be stored in a Set. All NaN values are equated (i.e. NaN is considered the same as NaN , even though NaN !== NaN ).

构造函数

Set(): 创建新的 Set 对象。

静态特性

get Set[@@species]

实例特性

Set.prototype.size: Returns the number of values in the Set 对象。

实例方法

Set.prototype.add( value ): 追加 value 到 Set object. Returns the Set 对象。
Set.prototype.clear(): Removes all elements from the Set 对象。
Set.prototype.delete( value ): Removes the element associated to the value and returns the value that Set.prototype.has( value ) would have previously returned. Set.prototype.has( value ) will return false afterwards.
Set.prototype.has( value ): Returns a boolean asserting whether an element is present with the given value in the Set object or not.

迭代方法

Set.prototype[@@iterator](): 返回新的 Iterator object that yields the 值 for each element in the Set object in insertion order.
Set.prototype.keys(): 返回新的 Iterator object that yields the values for each element in the Set object in insertion order. (For Sets, this is the same as the values() method.)
Set.prototype.values(): 返回新的 Iterator object that yields the 值 for each element in the Set object in insertion order. (For Sets, this is the same as the keys() method.)
Set.prototype.entries()
Set.prototype.forEach( callbackFn [, thisArg ]): 调用 callbackFn once for each value present in the Set object, in insertion order. If a thisArg parameter is provided, it will be used as the this value for each invocation of callbackFn .

范例

使用 `Set` object

let mySet = new Set()
mySet.add(1)           // Set [ 1 ]
mySet.add(5)           // Set [ 1, 5 ]
mySet.add(5)           // Set [ 1, 5 ]
mySet.add('some text') // Set [ 1, 5, 'some text' ]
let o = {a: 1, b: 2}
mySet.add(o)
mySet.add({a: 1, b: 2})   // o is referencing a different object, so this is okay
mySet.has(1)              // true
mySet.has(3)              // false, since 3 has not been added to the set
mySet.has(5)              // true
mySet.has(Math.sqrt(25))  // true
mySet.has('Some Text'.toLowerCase()) // true
mySet.has(o)       // true
mySet.size         // 5
mySet.delete(5)    // removes 5 from the set
mySet.has(5)       // false, 5 has been removed
mySet.size         // 4, since we just removed one value
console.log(mySet)
// logs Set(4) [ 1, "some text", {…}, {…} ] in Firefox
// logs Set(4) { 1, "some text", {…}, {…} } in Chrome

Iterating Sets

// iterate over items in set
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet) console.log(item)
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet.keys()) console.log(item)
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet.values()) console.log(item)
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
// (key and value are the same here)
for (let [key, value] of mySet.entries()) console.log(key)
// convert Set object to an Array object, with Array.from
let myArr = Array.from(mySet) // [1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}]
// the following will also work if run in an HTML document
mySet.add(document.body)
mySet.has(document.querySelector('body')) // true
// converting between Set and Array
mySet2 = new Set([1, 2, 3, 4])
mySet2.size                    // 4
[...mySet2]                    // [1, 2, 3, 4]
// intersect can be simulated via
let intersection = new Set([...set1].filter(x => set2.has(x)))
// difference can be simulated via
let difference = new Set([...set1].filter(x => !set2.has(x)))
// Iterate set entries with forEach()
mySet.forEach(function(value) {
  console.log(value)
})
// 1
// 2
// 3
// 4

Implementing basic set operations

function isSuperset(set, subset) {
    for (let elem of subset) {
        if (!set.has(elem)) {
            return false
        }
    }
    return true
}
function union(setA, setB) {
    let _union = new Set(setA)
    for (let elem of setB) {
        _union.add(elem)
    }
    return _union
}
function intersection(setA, setB) {
    let _intersection = new Set()
    for (let elem of setB) {
        if (setA.has(elem)) {
            _intersection.add(elem)
        }
    }
    return _intersection
}
function symmetricDifference(setA, setB) {
    let _difference = new Set(setA)
    for (let elem of setB) {
        if (_difference.has(elem)) {
            _difference.delete(elem)
        } else {
            _difference.add(elem)
        }
    }
    return _difference
}
function difference(setA, setB) {
    let _difference = new Set(setA)
    for (let elem of setB) {
        _difference.delete(elem)
    }
    return _difference
}
// Examples
let setA = new Set([1, 2, 3, 4])
let setB = new Set([2, 3])
let setC = new Set([3, 4, 5, 6])
isSuperset(setA, setB)          // => true
union(setA, setC)               // => Set [1, 2, 3, 4, 5, 6]
intersection(setA, setC)        // => Set [3, 4]
symmetricDifference(setA, setC) // => Set [1, 2, 5, 6]
difference(setA, setC)          // => Set [1, 2]

Relation with `Array` 对象

let myArray = ['value1', 'value2', 'value3']
// Use the regular Set constructor to transform an Array into a Set
let mySet = new Set(myArray)
mySet.has('value1')     // returns true
// Use the spread operator to transform a set into an Array.
console.log([...mySet]) // Will show you exactly the same Array as myArray

Remove duplicate elements from the array

// Use to remove duplicate elements from the array
const numbers = [2,3,4,4,2,3,3,4,4,5,5,6,6,7,5,32,3,4,5]
console.log([...new Set(numbers)])
// [2, 3, 4, 5, 6, 7, 32]

Relation with `字符串`

let text = 'India'
let mySet = new Set(text)  // Set ['I', 'n', 'd', 'i', 'a']
mySet.size  // 5
//case sensitive & duplicate ommision
new Set("Firefox")  // Set(7) [ "F", "i", "r", "e", "f", "o", "x" ]
new Set("firefox")  // Set(6) [ "f", "i", "r", "e", "o", "x" ]

规范

规范
ECMAScript (ECMA-262) The definition of 'Set' 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
`Set`	Chrome 38	Edge 12	Firefox 13	IE 11	Opera 25	Safari 8	WebView Android 38	Chrome Android 38	Firefox Android 14	Opera Android 25	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.
`Set()` 构造函数	Chrome 38	Edge 12	Firefox 13	IE 11	Opera 25	Safari 8	WebView Android 38	Chrome Android 38	Firefox Android 14	Opera Android 25	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.
`add`	Chrome 38	Edge 12	Firefox 13	IE 部分支持 11 部分支持 11 Returns 'undefined' instead of the 'Set' object.	Opera 25	Safari 8	WebView Android 38	Chrome Android 38	Firefox Android 14	Opera Android 25	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.
`clear`	Chrome 38	Edge 12	Firefox 19	IE 11	Opera 25	Safari 8	WebView Android 38	Chrome Android 38	Firefox Android 19	Opera Android 25	Safari iOS 8	Samsung Internet Android 3.0	nodejs 0.12
`delete`	Chrome 38	Edge 12	Firefox 13	IE 11	Opera 25	Safari 8	WebView Android 38	Chrome Android 38	Firefox Android 14	Opera Android 25	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.
`entries`	Chrome 38	Edge 12	Firefox 24	IE No	Opera 25	Safari 8	WebView Android 38	Chrome Android 38	Firefox Android 24	Opera Android 25	Safari iOS 8	Samsung Internet Android 3.0	nodejs 0.12
`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
`has`	Chrome 38	Edge 12	Firefox 13	IE 11	Opera 25	Safari 8	WebView Android 38	Chrome Android 38	Firefox Android 14	Opera Android 25	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.
Key equality for -0 and 0	Chrome 38	Edge 12	Firefox 29	IE No	Opera 25	Safari 9	WebView Android 38	Chrome Android 38	Firefox Android 29	Opera Android 25	Safari iOS 9	Samsung Internet Android 3.0	nodejs 4.0.0
`size`	Chrome 38	Edge 12	Firefox 19 19 From Firefox 13 to Firefox 18, the `size` property was implemented as a `Set.prototype.size()` method, this has been changed to a property in later versions conform to the ECMAScript 2015 specification.	IE 11	Opera 25	Safari 8	WebView Android 38	Chrome Android 38	Firefox Android 19 19 From Firefox 13 to Firefox 18, the `size` property was implemented as a `Set.prototype.size()` method, this has been changed to a property in later versions conform to the ECMAScript 2015 specification.	Opera Android 25	Safari iOS 8	Samsung Internet Android 3.0	nodejs 0.12
`值`	Chrome 38	Edge 12	Firefox 24	IE No	Opera 25	Safari 8	WebView Android 38	Chrome Android 38	Firefox Android 24	Opera Android 25	Safari iOS 8	Samsung Internet Android 3.0	nodejs 0.12
`@@iterator`	Chrome 43	Edge 12	Firefox 36 36 不支持 27 — 36 Alternate Name A placeholder property named `@@iterator` 被使用。 Alternate Name Uses the non-standard name: `@@iterator` 不支持 17 — 27 Alternate Name A placeholder property named `iterator` 被使用。 Alternate Name Uses the non-standard name: `iterator`	IE No	Opera 30	Safari 9	WebView Android 43	Chrome Android 43	Firefox Android 36 36 不支持 27 — 36 Alternate Name A placeholder property named `@@iterator` 被使用。 Alternate Name Uses the non-standard name: `@@iterator` 不支持 17 — 27 Alternate Name A placeholder property named `iterator` 被使用。 Alternate Name Uses the non-standard name: `iterator`	Opera Android 30	Safari iOS 9	Samsung Internet Android 4.0	nodejs 0.12
`@@species`	Chrome 51	Edge 13	Firefox 41	IE No	Opera 38	Safari 10	WebView Android 51	Chrome Android 51	Firefox Android 41	Opera Android 41	Safari iOS 10	Samsung Internet Android 5.0	nodejs 6.5.0 6.5.0 6.0.0 Disabled Disabled From version 6.0.0: this feature is behind the `--harmony` runtime flag.

图例

完整支持
部分支持
不支持

用户必须明确启用此特征。

另请参阅

元数据

最后修改： Aug 2, 2020

在此页

描述