ES6 基本使用

1.let  const 声明变量

let i = 1;      //不可重复声明，不变量提升
const j = 100;  //只读
var k = 20;

console.log(i,j,k)

2.对象优化

let person = {id:1,name:'jack'}

let peson2 = Object.assign(person)

console.log(person,peson2)//{ id: 1, name: 'jack' } { id: 1, name: 'jack' }

person.id=10  //浅复制，会更新

console.log(person,peson2)//{ id: 10, name: 'jack' } { id: 10, name: 'jack' }

let person = {id:1,name:'jack'}

let person2 = {...person}

console.log(person,person2)  //{ id: 1, name: 'jack' } { id: 1, name: 'jack' }

person.id=20  //深复制，不会更新

console.log(person,person2) //{ id: 20, name: 'jack' } { id: 1, name: 'jack' }

let t = {age:20}
let person3 = {...person,t}  //合并对象

console.log(person3)//{ id: 20, name: 'jack', t: { age: 20 } }

let show = function (i) {
    console.log(i)
}

show(100);  // 100

let show2 = (i)=>{console.log(i)}  //箭头函数

show2(200);  // 200

let show3 = (...i)=>{
    console.log(i)
    i.map((item)=>{    console.log(item)})
}
show3(1,10);  // [ 1, 10 ]
show3();  // []

3.模块化：export  import

let add = function (i, j) {
    return i + j;
}

let person = {
    id: 1,
    name: 'jack'
}

export {
    person,
    add
}

import {add,person} from './add.js'
let sum = add(10, 50)

console.log(person,sum)

 4.字符串

let s1 = 'hello,world';
//传统字符串叠加
let s2 = "111" +
    "aaa" +
    "bbb"
//模板，换行符合，都在字符串内
let s3 = `11
            aa
            bb`

let s4 = `${s1} 你好`   //字符串模板，格式：${}
console.log(s1,s2,s3,s4)

console.log(s1.startsWith("hello"))  //true
console.log(s1.startsWith("1hello"))  //false

console.log(s1.endsWith("world"))//true
console.log(s1.endsWith("world2"))//false

console.log(s1.includes("world"))//true