javascript的浅拷贝与深拷贝

平时使用数组复制时，我们大多数会使用‘=’，这只是浅拷贝，存在很多问题。比如

    let arr = [1,2,3,4,5];
let arr2 = arr;
    console.log(arr)  //[1, 2, 3, 4, 5]
    console.log(arr2) //[1, 2, 3, 4, 5]

    arr[0] = 6;
    console.log(arr) //[6, 2, 3, 4, 5]
    console.log(arr2) //[6, 2, 3, 4, 5]

    arr2[4] = 7;
    console.log(arr) //[6, 2, 3, 4, 7]
    console.log(arr2) //[6, 2, 3, 4, 7]

很明显，浅拷贝下，拷贝和被拷贝的数组会相互受到影响。所以，必须要有一种不受影响的方法，那就是深拷贝。

深拷贝的实现方式有很多种。

一：for循环实现深拷贝

  //for循环copy
    function copy(arr) {
let cArr = []
for(let i = 0; i < arr.length; i++){
            cArr.push(arr[i])
        }
return cArr;
    }

let arr3 = [1,2,3,4];
let arr4 = copy(arr3) //[1,2,3,4]
    console.log(arr4) //[1,2,3,4]

    arr3[0] = 5;
    console.log(arr3) //[5,2,3,4]
    console.log(arr4) //[1,2,3,4]

二：slice方法实现深拷贝

//slice实现深拷贝
let arr5 = [1,2,3,4];
let arr6 = arr5.slice(0);
    arr5[0] = 5;
    console.log(arr5); //[5,2,3,4]
    console.log(arr6); //[1,2,3,4]

三：concat实现深拷贝

//concat实现深拷贝
let arr7 = [1,2,3,4];
let arr8 = arr7.concat();
    arr7[0] = 5;
    console.log(arr7); //[5,2,3,4]
    console.log(arr8); //[1,2,3,4]

四：es6扩展运算实现深拷贝

//es6扩展运算实现深拷贝
let arr9 = [1,2,3,4];
let [...arr10] = arr9;
    arr9[0] = 5;
    console.log(arr9) //[5,2,3,4]
    console.log(arr10) //[1,2,3,4]

五：对象的循环深拷贝

//    循环copy对象

let obj = {
id:'0',
name:'king',
sex:'man'
    }

let obj2 = copy2(obj)

function copy2(obj) {
let cObj = {};
for(var key in obj){
            cObj[key] = obj[key]
        }

return cObj
    }

console.log(obj) //{id: "0", name: "king", sex: "man"}
console.log(obj2) //{id: "0", name: "king", sex: "man"}

六：对象转换成json实现深拷贝

//转换成json

    let obj3 = JSON.parse(JSON.stringify(obj));
    console.log(obj3) //{id: "0", name: "king", sex: "man"}

七：es6扩展运算实现深拷贝

let {...obj4}= obj
    console.log(obj4) //{id: "0", name: "king", sex: "man"}

总结：深刻理解javascript的深浅拷贝，可以灵活的运用数组，并且可以避免很多bug。