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function 函数名(参数) {
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    // 函数体
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    return 结果;
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}

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function add(a, b) {
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    return a + b;
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}

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函数名(实参);

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add(1, 2);     // 返回 3

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add('a', 'b');  // 返回 ab
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add(4, 5, 6);   // 返回 9, 第三个参数没有被用到, 不会报错
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add(1);      // 返回 NaN, 这时 b 没有定义是 undefined, undefined 做数学运算结果就是 NaN

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void pagination(int page = 1, int size = 10) {
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    std::cout << page << " " << size << std::endl;
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}

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function pagination(page = 1, size = 10) {
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    console.log(page, size);
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}

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(function (参数) {
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    // 函数体
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    return 结果;
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})

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(function(a,b){
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    return a + b;
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})

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(function(a,b){
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    return a + b;
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})(1,2)

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<p id="p1">点我啊</p>

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document.getElementById("p1").onclick = (function(){
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    console.log("鼠标单击了...");
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});

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(参数) => {
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    // 函数体
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    return 结果;
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}

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document.getElementById("p1").onclick = () =>  console.log("aa");

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function abc() {
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    console.log("bb");
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}
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document.getElementById("p1").onclick = abc;

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ƒ abc()
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    arguments: null
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    caller: null
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    length: 0
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    name: "abc"
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    ➡prototype: {constructor: ƒ}
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    [[FunctionLocation]]: VM1962:1
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    ➡[[Prototype]]: ƒ ()
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    ➡[[Scopes]]: Scopes[1]

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function a() {
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    console.log('a')
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}
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function b(fn) {          // fn 将来可以是一个函数对象
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    console.log('b')
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    fn();                 // 调用函数对象
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}
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b(a)

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function c() {
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    console.log("c");
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    function d() {
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        console.log("d");
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    }
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    return d;
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}
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c()()

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function a() {
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    function b() {
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    }
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}

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function c() {
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    var z = 30;
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}
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var x = 10;
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function a() {
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    var y = 20;
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    function b() {
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        // 看这里
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        console.log(x, y);
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    }
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    b();
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}
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a();

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var x = 10;
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function a() {
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    var y = 20;
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    function b() {
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        console.log(x,y);
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    }
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    return b;
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}
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a()();  // 在外面执行了 b

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let x = 10;
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if(true) {
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    let y = 20;
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    function b() {
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        console.log(x,y);
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    }
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    console.dir(b);
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}

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var x = 10;
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if(true) {
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    var y = 20;
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    function b() {
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        console.log(x,y);
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    }
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    console.dir(b);
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}

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var e = 10;
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if(true) {
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    var e = 20;
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    console.log(e);  // 打印 20
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}
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console.log(e);    // 因为是同一个变量，还是打印 20

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let e = 10;
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if(true) {
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    let e = 20;
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    console.log(e);  // 打印 20
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}
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console.log(e);    // 打印 10

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var e = 10;
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if(true) {
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    function b() {
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        var e = 20;
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      console.log(e);
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    }
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    b();
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}
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console.log(e);

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let obj = {
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    属性名: 值,
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    方法名: 函数,
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    get 属性名() {},
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    set 属性名(新值) {}
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}

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let stu1 = {
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    name: "小明",
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    age: 18,
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    study: function(){
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        console.log(this.name + "爱学习");
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    }
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}

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let name = "小黑";
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let age = 20;
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let study = function(){
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    console.log(this.name + "爱学习");
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}
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let stu2 = { name, age, study }

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let stu3 = {
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    name: "小白",
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    age: 18,
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    study(){
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        console.log(this.name + "爱学习");
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    }
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}

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let stu4 = {
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    _name: null, /*类似于C++ 中私有成员变量*/
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    get name() {
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        console.log("进入了get");
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        return this._name;
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    },
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    set name(name) {
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        console.log("进入了set");
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        this._name = name;
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    }
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}

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stu4.name = "小白"
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console.log(stu4.name)

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let stu = {name:'张三'};
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stu.age = 18;          // 添加属性
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delete stu.age;          // 删除属性
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stu.study = function() {    // 添加方法
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    console.log(this.name + "在学习");
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}

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let stu = {_name:null};
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Object.defineProperty(stu, "name", {
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    get(){
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        return this._name;
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    },
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    set(name){
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        this._name = name;
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    }
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});

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function study(subject) {
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    console.log(this.name + "在学习 " + subject)
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}

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study("js");  // 输出 在学习 js

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let stu = {
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    name:"小白",
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    study
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}

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stu.study('js');   // 输出 小白在学习 js

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let stu = {name:"小黑"};
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study.call(stu, "js");  // 输出 小黑在学习 js

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let stu = {
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    name: "小花",
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    friends: ["小白","小黑","小明"],
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    play() {
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        this.friends.forEach(function(e){
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            console.log(this.name + "与" + e + "在玩耍");
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        });
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    }
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}
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stu.play()

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与小白在玩耍
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与小黑在玩耍
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与小明在玩耍

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let stu = {
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    name: "小花",
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    friends: ["小白","小黑","小明"],
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    play() {
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        this.friends.forEach(e => {
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            console.log(this.name + "与" + e + "在玩耍");
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        })
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    }
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}

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小花与小白在玩耍
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小花与小黑在玩耍
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小花与小明在玩耍

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let stu = {
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    name: "小花",
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    friends: ["小白","小黑","小明"],
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    play() {
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        let me = this;
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        this.friends.forEach(function(e){
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            console.log(me.name + "与" + e + "在玩耍");
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        });
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    }
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}

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let father = {
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    f1: '父属性',
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    m1: function() {
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        console.log("父方法");
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    }
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}
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let son = Object.create(father);
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console.log(son.f1);  // 打印 父属性
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son.m1();        // 打印 父方法

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function cons(f2) {
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    // 创建子对象(this), 给子对象提供属性和方法
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    this.f2 = f2;
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    this.m2 = function () {
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        console.log("子方法");
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    }
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}
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// cons.prototype 就是父对象
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cons.prototype.f1 = "父属性";
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cons.prototype.m1 = function() {
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    console.log("父方法");
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}

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let son = new cons("子属性")

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{
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    "name":"张三",
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    "age":18
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}

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{
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    name:"张三",
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    age:18
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}

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JSON.parse(json字符串);  // 返回js对象
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JSON.stringify(js对象);  // 返回json字符串