What are the new features of es6?

New features of ES6

1, let and const

https: //m.sbmmt.com/js-tutorial-499866.html

2. symbol

const a = Symbol(); console.log(a); //Symbol() //因为Symbol是基本数据类型，而不是对象，不能 new 。 const a = new Symbol();//报错，Symbol is not a constructor

const a = Symbol();const b = Symbol();

3. Template String

Before ES6, handling template strings:
• Build templates by "\" and " "
  
For ES6:
• Use
  ${}to define;backtick
  (``)can be done directly;

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3.1 New string method (supplementary)

• includes()Determine whether the string contains the parameter string and return a boolean value.
• startsWith() / endsWith(), determine whether the string starts or ends with the parameter string. Returns a boolean value. These two methods can have a second parameter, a number, indicating the position to start the search.

let str = 'blue,red,orange,white';str.includes('blue'); //truestr.startsWith('blue'); //true str.endsWith('blue'); //false

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• repeat()The method returns a new string the specified number of times.

console.log('hello'.repeat(2)); //'hellohello'

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• padStart()/padEnd(), use the parameter string to complete the string from the front or back according to the given length, and return a new string.

let arr = 'hell';console.log(arr.padEnd(5,'o')); //'hello'console.log(arr.padEnd(6,'o')); //'helloo'console.log(arr.padEnd(6)); //'hell ',如果没有指定将用空格代替 console.log(arr.padStart(5,'o')); //'ohell'

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4. Destructuring expression

arrayorobject, and then assigns values to the variables in it.
String, and the newMapandSetadded in ES6 can all use destructuring expressions

4.1 Array destructuring

let [a,b,c] = [1,2,3];console.log(a,b,c); //1,2,3 let [a,b,c] = [1,,3];console.log(a,b,c); //1,undefined,3 let [a,,b] = [1,2,3];console.log(a,b);//1,3 let [a,..b] = [1,2,3]; //...是剩余运算符，表示赋值运算符右边除第一个值外剩余的都赋值给b console.log(a,b); //1,[2,3]

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4.2 Object destructuring

let obj = { name: "ren", age: 12, sex: "male" };let { name, age, sex } = obj;console.log(name, age, sex); //'ren' 12 'male'let { name: myName, age: myAge, sex: mySex } = obj; //自定义变量名console.log(myName, myAge, mySex); //'ren' 12 'male'

5. Object aspect

##5.1 Map and SetMap and Set belong to Newly added objects in es6

5.1.1 MapThe Map object is used to save key-value pairs. Any value supported by JavaScript can be used as a key. Or a value.

object keys can only be
• strings

  or ES6symbolvalues, while Map can be any value.

The Map object has a
• size attribute

  , which stores the number of key-value pairs, while the object object has no similar attribute.

  let myMap = new Map([['name','ren'],['age',12]]);console.log(myMap); //{'name'=>'ren','age'=>12}myMap.set('sex','male');console.log(myMap); //{'name'=>'ren','age'=>12,'sex'=>'male'}console.log(myMap.size); //3myMap.get('name'); //'ren'myMap.has('age'); //truemyMap.delete('age'); //truemyMap.has('age'); //falsemyMap.get('age'); //undefined

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5.1.2 Setcan be understood as the Set collection object of the backend

each element is unique
.

let mySet = new Set([1,2,3]); //里面要传一个数组，否则会报错console.log(mySet); //{1,2,3}mySet.add(4);console.log(mySet); //{1,2,3,4}mySet.delete(1); //truemySet.has(1); //falseconsole.log(mySet); //{2,3,4}

, you can easilyachieve duplication of arrays

let arr = [1,1,2,3,4,4];let mySet = new Set(arr); let newArr = Array.from(mySet);console.log(newArr); //[1,2,3,4]

let arr = [1, 2, 3];let obj = { double(n) { return n * 2; }}console.log(Array.from(arr, function (n){ return this.double(n);}, obj)); // [2, 4, 6]

let arr = [1,33,44,22,6,9]let ary = arr.includes(22)console.log(ary)

let arr = [1,33,44,2,6,9]let a1= []arr.forEach((v, i)=>{ if (v > 10) { a1.push(arr[i]) } })console.log(a1) [33,44]let a2= arr.find(v => v > 10)console.log(a2)

let arr = [1,33,44,2,6,9]let a= arr.find(v => v > 10)console.log(a) // 33

let arr = [1,2,3,4,6,11]let newarr = arr.some(function(v){ return v > 10})console.log(newarr) //truelet newarr2 = arr.every(function(v){ return v > 10})console.log(newarr2) //false

const obj1 = {};const obj2 = {};console.log(Object.is(obj1, obj2)); // falseconst obj3 = {};const value1 = obj3;const value2 = obj4;console.log(Object.is(value1, value2)); // true

const obj1 = { a: 1 };const obj2 = { b: 2 };const obj3 = { a:5 , c: 3 };//对象合并，把后面对像合并到第一个对象，对象里相同的属性会覆盖Object.assign(obj1, obj2, obj3);console.log(obj1); // { a: 5, b: 2 , c:3}

let add = (a,b) => { return a+b;}let print = () => { console.log('hi');}let fn = a => a * a; //当只有一个参数时，括号可以省略，函数体只有单行return语句时，大括号也可以省略。

var age = 123; let obj = { age:456, say:() => { console.log(this.age); //this指向window } };obj.say(); //123

import ‘模块名称’ from ‘路径’；import ‘路径’；

let name = 'ren',age = 12;export {name,age}; //注意：变量需要用大括号包裹，然后才能向外输出

1.防止命名冲突

2.复用性强