js深拷贝和浅拷贝

一浅拷贝

1.for···in只循环第一层

function simpleCopy(obj1) {
    var obj2 = Array.isArray(obj1)?[]:{};
    for (let i in obj1){
        obj2[i] = obj1[i];
    }
    return obj2;
}
var obj1 = {a:1,b:2,c:{d:3}};
var obj2 = simpleCopy(obj1);
debugger
obj2.a = 3;
obj2.c.d =4;
console.log(obj1);
console.log(obj2);
2.Object.assign方法

 var obj = {
       a:1,
       b:2
   }
   var obj1 = Object.assign(obj);;
   obj1.a = 3;
   console.log(obj.a);
3.直接用=赋值

let a=[0,1,2,3,4];
 b=a;
 console.log(a===b);
 a[0] = 1;
 console.log(a,b);
二、深拷贝
1.采用递归去拷贝所有层级属性

function deepClone(obj) {
    let objClone = Array.isArray(obj)?[]:{};
    if (obj && typeof obj ==="object"){
        for (key in obj){
            if (obj.hasOwnProperty(key)){
                if (obj[key] && typeof obj[key] ==="object"){
                    objClone[key] =deepClone(obj[key]);
                } else {
                    objClone[key]=obj[key];
                }
            }
        }
    }
    return objClone
}
let a=[1,2,3,4,{b:4}],
b=deepClone(a);
a[0] = 2;
a[4].b=5;
console.log(a,b);
2.通过json对象来实现深拷贝

function deepClone2(obj) {
        var _obj = JSON.stringify(obj),objClone=JSON.parse(_obj);
        return objClone;
    }
    let a=[1,2,3,4,{b:4}],
        b=deepClone2(a);
    a[0] = 2;
    a[4].b=5;
    console.log(a,b);

缺点：无法实现对对象中方法的深拷贝,会显示为undefind

3.通过jQuery的extend方法实现深拷贝

　　var array =[1,2,3,4];
    var newArray = $.extend(true,[],array);
    newArray[0] = 5;
    console.log(array,newArray);

4.手动实现深拷贝

let obj1 = {
     a:1,
     b:2
 }
 let obj2 = {
     a:obj1.a,
     b:obj1.b
 }
 obj2.a = 3;
 console.log(obj1,obj2);
5.如果对象的value时基本类型的话，也可以用object.assign()来实现深拷贝，但是要把它赋值给一个空对象

var obj = {
        a:1,b:2
    }
    var obj1 = Object.assign({},obj);
    obj1.a = 3;
    console.log(obj,obj1);
6.用slice实现对数组的深拷贝

var arr1 = ["1","2","3"];
    var arr2 = arr1.slice(0);
    arr2[1] = "9";
    console.log("数组的原始值："+arr1);
    console.log("数组的新值:"+arr2);
7.用concat实现对数组的深拷贝，当数组里面的值是基本数据类型，比如String,Number,Boolean时，属于深拷贝

 var arr1 = ["1","2","3"];
 var arr2 = arr1.concat();
 arr2[1] = "9";
 console.log(arr1,arr2);

//当数组里面的值是引用数据类型，比如Object,Array时，属于浅拷贝

var arr1 = [{a:1},{b:2},{c:3}];
   var arr2 = arr1.concat();
   arr2[0].a ="9";
   console.log(arr1,arr2);
8.直接使用 var newObj = Object.create(oldObj)可以达到深拷贝的效果

function deepClone(initalObj,finalObj) {
     var obj = finalObj||{};
     for (var i in initalObj){
         var prop = initalObj[i];
         if (prop ===obj){
             continue;
         }
         if (typeof prop ==='object'){
             obj[i] =(prop.constructor ===Array)?[]:Object.create(prop);
         } else{
             obj[i] = prop;
         }
     }
     return obj;
 }
9.使用扩展运算符实现深拷贝

var car = {brand:"BMW",price:"380000",length:"5米" }
    var car1 = {...car,price:"50000"};
    console.log(car,car1);
10.lodash函数库实现深拷贝
11Reflect法