摘要：基礎(chǔ)實(shí)踐和和的區(qū)別輸出輸出猜猜是否報錯，以及輸出什么常量模板字符串普通字符串我是一個好人多行字符串我還是可以換行的字符串猜猜的長度是多少猜猜是否相等插入變量張三你好，很高興認(rèn)識你，我是，我的性別是男，我今年歲，我想說李四延伸思考解構(gòu)賦值數(shù)組

var a = 1;
window.a;    // 輸出：1
let b = 2;
window.b;    // 輸出：undefined

{
    let a = 1;
    // let a = 2;
    var b = 2;
}

console.log(a);
console.log(b);

let a = 1;
{
    console.log(a);
    let a = 2;
}

let i = "a";

for(let i = 0; i < 10; i++){
    // let i = "b";
    console.log(i);
}

// 猜猜是否報錯，以及輸出什么

    const a = [1,2,3];
    const b = a;
    const c = [1,2,3];

    `我是一個好人`

    console.log(`我還是可以
                換行的字符串`);

let a = `1
2
3
4`;

a.length //猜猜a的長度是多少？

let b = "1
2
3
4";

a === b //猜猜是否相等？

    let name = "張三";
    let age = 12;
    function say(name){
        return "你好，很高興認(rèn)識你，" + name;
    }
    
    console.log(`我是${name}，我的性別是：${ "男" }，我今年 ${ age * 2 }歲，我想說： ${ say("李四") }`);

let a = "abc";
let b = new String("abc");
a == b?
a === b?

let a = 1, b = 2, c = 3;

let [a, b, c] = [1, 2, 3];

let [a, ...b] = [1, 2, 3, 4];

let [a = 1] = [2];

let [a = 1] = [null];

let [a = 1] = [undefined];

let [a] = [null];

let [a] = [];

let {a, b} = {a: 1, b: 2 };

let {a : newA, b: newB} = {a: 1, b: 2 };

let {a = 1} = {};

let {a = 1} = {a:2};

1、先兩句一起執(zhí)行：
    let a = 1;
    {a} = {a: 2}

2、分開一條一條執(zhí)行
    let a = 1;
    
    {a} = {a: 2}

3、反過來執(zhí)行
    {a} = {a: 2}
    let a = 1;
    
    a ?
    window.a ?
    上面的a 和 window.a 各輸出什么？

let a = 1;
({a} = {a: 2})
如果這樣的兩句一起執(zhí)行呢？

用途

交換變量的值

    let a = 1;
    let b = 2;
    [a, b] = [b, a];

從函數(shù)返回多個值

    function example() {
      return [1, 2, 3];
    }
    let [a, b, c] = example();

    function example() {
      return {
        a: 1,
        b: 2
      };
    }
    let {a, b} = example();

函數(shù)參數(shù)的定義

    function example([a, b, c]) {
         console.log(a, b, c); 
    }
    
    example([1, 2, 3]);

提取JSON數(shù)據(jù)

    let myDataList = {
      name: "張三",
      sex: "男",
      age: "24"
    };
    
    let { name, sex, age} = myDataList;

函數(shù)參數(shù)的默認(rèn)值

    let throwMyErr = (errName) => {
        throw new Error(`請傳入?yún)?shù) ${errName}`);
    }
    
    let example = (name = throwMyErr("name")) => {
        console.log(name);
    }

    let example = x => x * 2;

    let myObj = {
        funA : function(){
            setTimeout(function(){
                console.log(this);
            }, 500);
        }
    }
    
    let myObj = {
        funA : function(){
            setTimeout(() => {
                console.log(this);
            }, 500);
        }
    }

    function SayHellowES5 (){
        this.name = "SARS";
    }
    
    SayHellowES5.prototype.say = function () {
        console.log(this.name);
    };

    class SayHellow {
      constructor() {
        this.name = "SARS";
      }
      say(){
        console.log(this.name);
      }
    }
    
    typeof SayHellow
    SayHellow === SayHellow.prototype.constructor

    var a = new SayHellow();
    a === SayHellow ?
    a.constructor === SayHellow ?

    var b = new SayHellow();
    a.__proto__ === b.__proto__ ?
    原型是否相等？

    b.__proto__.say2 = function(){
        alert("say2");
    }
    
    a.say2() ?
    
    思考 this 到底指的哪？原型呢？同樣下面的繼承是否也一樣？
    （確認(rèn)下節(jié)課內(nèi)容）

    class SayBey extends SayHellow{
      sayBey(){
        console.log("beybey!");
      }
    }

    class toBey extends SayHellow{
      sayBey(){
        console.log(`${this.name} beybey!`);
      }
    }

    class toBey2 extends SayHellow{
      constructor() {
        this.sex = "女";
      }
      sayBey(){
        console.log(`${this.sex} beybey!`);
      }
    }
    //想想為什么報錯？

    export let myLetA = 1;
    export let myLetB = 2;
    export let example = () => {
        alert("SARS");
    }

    let myLetA = 1;
    let myLetB = 2;
    let example = () => {
        alert("SARS");
    }
    export {myLetA, myLetB, example as name};

    // 正確
    var a = 1;
    export default a;
    
    // 錯誤
    export default var a = 1;

    import {myLetA, myLetB, example as name} from "./main";
    import SARS from "./main";