数组浅拷贝和深拷贝的实现方法 - 《javascript》

1.数组的浅拷贝

var a = [1,2,3,4]
var b = a

2.一维数组的深拷贝

1.splice方法

var a = [1,2,3,4]
var b = a.slice()
a[0] = 5
console.log(a) // [5,2,3,4]
console.log(b) // [1,2,3,4]

2.cocat方法

var a = [1,2,3,4]
var b = a.concat()
a[0] = 5
console.log(a) // [5,2,3,4]
console.log(b) // [1,2,3,4]

3.循环

var a = [1,2,3,4]
var b = cloneArray(a);
a[0] = 5
console.log(a) // [5,2,3,4]
console.log(b) // [1,2,3,4]
function cloneArray(arr) {
  const newArray = []
    for(let i = 0; i < arr.length; i++) {
    newArray.push(arr[i])
  }
  return newArray
}

4.es6新特性之扩展运算符

 var a = [1,2,3,4]
 var b = [...a]
 a[0] = 5
console.log(a) // [5,2,3,4]
console.log(b) // [1,2,3,4]

5.es6新特性之Array.from

var a = [1,2,3,4]
var b = Array.from(a);
a[0] = 5;
console.log(a) // [5,2,3,4]
console.log(b) // [1,2,3,4]

3.多维数组的深拷贝

1.json.parse()和json.stringify()

var a = [1,[2,3],4]
var b = JSON.parse(JSON.stringify(a));
a[1][0] = 5;
console.log(a) // [1,[2,3],4]
console.log(b) // [1,[5,3],4]

拷贝的对象的值中如果有函数,undefined,symbol则经过JSON.stringify()序列化后的JSON字符串中这个键值对会消失
无法拷贝不可枚举的属性，无法拷贝对象的原型链
拷贝Date引用类型会变成字符串
拷贝RegExp引用类型会变成空对象
对象中含有NaN、Infinity和-Infinity，则序列化的结果会变成null
无法拷贝对象的循环应用(即obj[key] = obj)

2.循环+递归

var a = [1,[2,3],4]
var b = deepClone(a);
a[1][0] = 5
console.log(a);
console.log(b);
function deepClone(arr) {
    if(!arr || typeof arr !== 'object'){
    return arr
  }
  const newArr = []
  for(var key in arr) {
    if(typeof arr[key] ==='object'){
        newArr[key] = deepClone(arr[key])
    }else {
        newArr[key] = arr[key]
    }
  }
  return newArr
}