search
HomeWeb Front-endFront-end Q&AWhat are the new es6 data structures?
What are the new es6 data structures?Apr 15, 2022 pm 07:26 PM
es6data structure

The new structures are: 1. Symbol, which represents a unique value and is a function structure; 2. Set, which refers to a "set" structure, similar to an array, allowing the storage of unordered and non-repeated data; 3. WeakSet, similar to Set, the internal data cannot have duplicate values; 4. Map, refers to the "dictionary" structure, which can store mapping relationships.

What are the new es6 data structures?

The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.

ES6 new data structure

1, Symbol

Symbol isES6 One of the new basic data types in is a function. Each Symbol value returned from the Symbol function is unique, and the symbol value serves as the identifier of the object attribute and has its only purpose.

const s1 = Symbol()
const s2 = Symbol()
console.log(s1 === s2); // false

symbol as key

The first way is to add it directly to the literal of the object.

// symbol作为key
const obj = {
  [s1]:'abc',
  [s2]:'cc',
}

The second way is to add it by adding an array.

// 需要用数组方式来获取,不能通过点语法,否则会获取到字符串key
console.log(obj[s1]);

The third way is to add it through the defineProperty method in the object.

const s4=Symbol()
Object.defineProperty(obj,s4,{
  configurable:true,
  enumerable:true,
  writable:true,
  value:'ff'
})

Get the corresponding value through symbol

It needs to be obtained in array mode, not through dot syntax, otherwise the string key will be obtained.

console.log(obj[s1]);

symbol cannot be implicitly converted to type string.

Note: The parameter in the Symbol function is the symbol descriptor, which is a new feature in ES10

let Sym = Symbol("Sym")
alert(Sym)  // TypeError: Cannot convert a Symbol value to a string

We cannot alert one directly symbol object, but we can get the descriptor of the symbol object through toString or .description.

let sym = Symbol('a')
console.log(sym.description); // 'a'

Traversing symbol

cannot obtain symbol when using for traversal and object.keys Healthy, object also provides the getOwnPropertySymbols method, which is used to obtain the keys of all symbols in the object.

const sKeys=(Object.getOwnPropertySymbols(obj));
for(const skey of sKeys){
  console.log(obj[skey]);
}

Global symbol object registration

Sometimes, we may need the values ​​of multiple symbol to be consistent, we can pass symbol The static method provided for method passes in the same descriptor to make their values ​​consistent.

Symbol.for

This method searches the runtime symbol registry for an existing symbol using the given key and returns it if found. Otherwise, a new symbol is created in the global symbol registry using this key.

const sa=Symbol.for('cc')
const sb=Symbol.for('cc')
console.log(sa===sb); //true

Symbol.keyFor

This method is used to obtain the descriptor of the global symbol.

const key =Symbol.keyFor(sb)
console.log(key); // c

2. Set

Set object (similar to an array) allows you to store any data type, but the Value cannot be repeated.

const s1 = new Set()
s1.add(10)
s1.add(20)
s1.add(30)
s1.add(40)

console.log(s1) // Set(4) { 10, 20, 30, 40 }

s1.add(20)
console.log(s1) // Set(4) { 10, 20, 30, 40 }

Set common methods

Method Return value Description
size setThe number in the object Returns the number in the set object Quantity
add SetObject Add element
delete boolean Delete element
has boolean SetWhether this value exists in the object
clear None Clear the value in the Set object

##3. WeakSet

WeakSet is another data structure similar to Set, and the internal data cannot have duplicate values.

    The difference between it and
  • Set
    • WeakSet can only store object types, not basic data types
    • WeakSetIt is a weak reference to the element

Basic use

const weakSet = new WeakSet();
let obj = {
  name: "_island"
};

weakSet.add(obj);

WeakSet common methods

MethodReturn valueDescriptionAdd elementDelete element

关于遍历

WeakSet不能被遍历,因为它只是对对象进行弱引用,如果遍历去获取元素,有可能导致对象不能被GC回收。

所以WeakSet中的对象是不能获取的

4、Map

ES6新增的数据结构,用于存储映射关系。我们知道在JavaScript中对象中是不能用对象来作为key的。(假如我们把对象作为key,其内部会将对象转换为字符串[object object]

const obj1 = { name: "_island" };
const obj2 = { name: "QC2125" };
const obj3={
  [obj1]:'a',
  [obj2]:'b',
}

console.log(obj3);
// { '[object Object]': 'b' }

Map则可以把对象作为key进行存储,可以通过set方法添加到Map中,也直接通过字面量的方式添加。

const obj1 = { name: "_island" };
const obj2 = { name: "QC2125" };
const map = new Map();
map.set(obj1, "a");
map.set(obj2, "b");
console.log(map); // Map(2) { { name: '_island' } => 'a', { name: 'QC2125' } => 'b' }

// or
const map2 = new Map([[obj1,'a'],[obj2,'b']])

Map常用方法

add weaksetObject
delete boolean
has boolean weaksetWhether this value exists in the object
方法 返回值 说明
get 获取对应的元素 通过key获取对应元素
size Map对象中的数量 返回Map对象中的数量
set Map对象 添加元素
delete boolean 删除元素
has boolean Set对象中是否存在这个值
clear 清空Set对象中的值

遍历Map

通过foreach语句遍历Map

map2.forEach((item) => console.log(item));

通过for..of遍历Map

for ([val, key] of map2) {
  console.log(`${key}---${val}`);
}

5、WeakMap

Map类似,也是以键值对的形式存在的

  • 和Map的区别
    • WeakMapkey只能使用对象,不接受其他的类型作为key
    • WeakMapkey对对象是弱引用

基本使用

const weakMap = new WeakMap();
weakMap.set(obj, "a");
console.log(weakMap.get(obj)); // a

WeakMap常用方法

方法 返回值 说明
get weakmap对象 获取元素
delete boolean 删除元素
has boolean weaksmap对象中是否存在这个值

关于遍历

WeakSet一样,正因为它是弱引用,WeakMapkey是不可枚举的,如果key可枚举那其列表将会受GC影响。

【相关推荐:javascript视频教程web前端

The above is the detailed content of What are the new es6 data structures?. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
es6怎么判断是否为数组es6怎么判断是否为数组Apr 25, 2022 pm 06:43 PM

在es6中,可以利用“Array.isArray()”方法判断对象是否为数组,若判断的对象是数组,返回的结果是true,若判断对象不是数组,返回的结果是false,语法为“Array.isArray(需要检测的js对象)”。

es6中遍历跟迭代的区别是什么es6中遍历跟迭代的区别是什么Apr 26, 2022 pm 02:57 PM

es6中遍历跟迭代的区别是:遍历强调的是要把整个数据依次全部取出来,是访问数据结构的所有元素;而迭代虽然也是依次取出数据,但是并不保证取多少,也不保证把所有的数据取完,是遍历的一种形式。

es6中怎么判断两个对象是否相等es6中怎么判断两个对象是否相等Apr 19, 2022 pm 03:34 PM

在es6中,可用Object对象的is()方法来判断两个对象是否相等,该方法检测两个变量的值是否为同一个值,判断两个对象的引用地址是否一致,语法“Object.is(对象1,对象2)”;该方法会返回布尔值,若返回true则表示两个对象相等。

es6怎么将数字转为字符串es6怎么将数字转为字符串Apr 19, 2022 pm 06:38 PM

转换方法:1、利用“+”给数字拼接一个空字符,语法“数字+""”;2、使用String(),可把对象的值转换为字符串,语法“String(数字对象)”;3、用toString(),可返回数字的字符串表示,语法“数字.toString()”。

es6中assign的用法是什么es6中assign的用法是什么May 05, 2022 pm 02:25 PM

在es6中,assign用于对象的合并,可以将源对象的所有可枚举属性复制到目标对象;若目标对象与源对象有同名属性,或多个源对象有同名属性,则后面的属性会覆盖前面的属性,语法为“Object.assign(...)”

es6怎么改变数组数据es6怎么改变数组数据Apr 26, 2022 am 10:08 AM

改变方法:1、利用splice()方法修改,该方法可以直接修改原数组的内容,语法为“数组.splice(开始位置,修改个数,修改后的值)”;2、利用下标访问数组元素,并重新赋值来修改数组数据,语法为“数组[下标值]=修改后的值;”。

sort排序是es6中的吗sort排序是es6中的吗Apr 25, 2022 pm 03:30 PM

sort排序是es6中的;sort排序是es6中用于对数组的元素进行排序的方法,该方法默认不传参,按照字符编码顺序进行排序,排序顺序可以是字母或数字,并按升序或降序,语法为“array.sort(callback(a,b))”。

import as在es6中的用法是什么import as在es6中的用法是什么Apr 25, 2022 pm 05:19 PM

在es6中,import as用于将若干export导出的内容组合成一个对象返回;ES6的模块化分为导出与导入两个模块,该方法能够将所有的导出内容包裹到指定对象中,语法为“import * as 对象 from ...”。

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
1 months agoBy尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

SAP NetWeaver Server Adapter for Eclipse

SAP NetWeaver Server Adapter for Eclipse

Integrate Eclipse with SAP NetWeaver application server.

EditPlus Chinese cracked version

EditPlus Chinese cracked version

Small size, syntax highlighting, does not support code prompt function

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

VSCode Windows 64-bit Download

VSCode Windows 64-bit Download

A free and powerful IDE editor launched by Microsoft