深层拷贝与浅层拷贝

深拷贝(完美拷贝)：

① 如果是基本数据类型，直接返回；
② 如果是RegExp或者Data类型，返回对应类型；
③ 如果是复杂数据类型，递归；
④ 考虑循环引用的问题。

  function deepClone(obj, hash = new WeakMap) {
    
    
        if (obj instanceof RegExp) {
    
    
            return new RegExp(obj)
        }
        if (obj instanceof Date) {
    
    
            return new Date(obj)
        }
        if (obj == null || typeof obj !== 'object') {
    
    
            return obj
        }
        if (hash.has(obj)) {
    
    
            return hash.get(obj)
        }
        let a = new obj.constructor()
        hash.set(obj, a)
        
        for (let key in obj) {
    
    
            //递归
            if (obj.hasOwnProperty(key)) {
    
    
                a[key] = deepClone(obj[key], hash)
            }
        }
        return a
    }
    var show = {
    
    
        name: '小明',
        fn: function () {
    
     console.log(1) },
        age: null,
        pic: undefined,
    }
    var show2 = deepClone(show)
    show2.name = "Mary"
    console.log(show, show2)

浅拷贝（只能拷贝一层）：Object.assign和for in进行{ }和[ ]的拷贝。

//Object.assign()拷贝方法
    //拷贝{}
        a = {
    
    name:"张三"};
        b = Object.assign({
    
    },a);
        b.name = "李四";    //拷贝完之后进行改变属性，测试拷贝的属性值改变原数据是否改变。
        console.log(a,b);
        //输出:{name:"张三"} 
               {
    
    name:"李四"} (拷贝成功)
    //拷贝[]
        a = ["1","2","3"];
        b = Object.assign([],a);
        b[1]="hello";
        console.log(a,b)
        //输出:["1","2","3"] 
               ["1","hello","3"] (拷贝成功)

//for in拷贝方法
    var copy = function(a){
    
    
        var res = a.constructor();
        for(var key in a){
    
    
            if(a.hasOwnProperty(key)){
    
    
                res[key] = a[key]
            }
        }
        return res;
    }   
    a = {
    
    name:"123",people:{
    
    name:"456"}};
    b = copy(a);
    b.people.name="hello"; 
    a = ["a","b","c"];b = copy(a);
    b[1] = 0;//拷贝完之后进行改变属性，测试拷贝的属性值改变原数据是否改变。
    console.log(a,b)  
    //输出:["a","b","c"] 
           ["a","0","c"] (拷贝成功)