数组，对象深拷贝

数组深拷贝

1、for循坏

var arr = [1,2,3,4,5]
var arr2 = copyArr(arr)
function copyArr(arr) {
    let res = []
    for (let i = 0; i < arr.length; i++) {
     res.push(arr[i])
    }
    return res
}

2、数组slice 方法

var arr = [1,2,3,4,5]
var arr2 = arr.slice(0)
arr[2] = 5
console.log(arr)
console.log(arr2)

3、数组concat 方法

var arr = [1,2,3,4,5]
var arr2 = arr.concat()
arr[2] = 5
console.log(arr)
console.log(arr2)

4、ES6扩展运算符实现数组的深拷贝

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

对象深拷贝

1、万能的for循环实现对象的深拷贝

var obj = {
  name: 'FungLeo',
  sex: 'man',
  old: '18'
}
var obj2 = copyObj(obj)
function copyObj(obj) {
  let res = {}
  for (var key in obj) {
    res[key] = obj[key]
  }
  return res
}

2、转换成json再转换成对象实现对象的深拷贝

var obj = {
  name: 'FungLeo',
  sex: 'man',
  old: '18'
}
var obj2 = JSON.parse(JSON.stringify(obj))

3、扩展运算符实现对象的深拷贝

var obj = {
  name: 'FungLeo',
  sex: 'man',
  old: '18'
}
var { ...obj2 } = obj
obj.old = '22'
console.log(obj)
console.log(obj2)

4、深拷贝函数

var obj1 = {
    country: '中国',
    city: ['北京', '上海', '广州'],
    skincolr: 'yellow',
    date: 2007,
    friend: {
    name: "dot",
    age: null
}
}
//深复制，要想达到深复制就需要用递归
 function deepCopy(oldObj, newObj) {
    var newObj = newObj || {};
    for (var i in oldObj) {
        //用instanceof排除null的情况
        if (oldObj[i] instanceof Object) {
        //要考虑深复制问题了
        if (oldObj[i].constructor === Array) {
            //这是数组
            newObj[i] = [];
        } else {
            //这是对象
            newObj[i] = {};
        }
        deepCopy(oldObj[i], newObj[i]);
    } else {
        newObj[i] = oldObj[i];
    }
}
return newObj;
  }
  var obj2 = { name: 'obj2'};
  obj2 = deepCopy(obj1, obj2);
  console.log(obj2);

数组，对象深拷贝函数

function deepClone(obj) {
        let objClone = Array.isArray(obj) ? [] : {}
 
        if (obj && typeof obj == 'object') {
          for (key in obj) { 
 
            // for-in遍历的是原型链，需要用hasOwnProperty 判断是否是自有属性
            if (obj.hasOwnProperty(key)) {
              //   判断obj子元素是否为对象。如果是，则递归复制
              if (obj[key] && obj[key] === 'object') {
                objClone[key] = deepClone(obj[key])
              } else {
                // 如果不是，简单复制
                objClone[key] = obj[key]
              }
            }
          }
          return objClone
        } else {
          //如果obj不是对象，那么直接返回值就可以了
          return obj
        }
      }