js 复制对象的深复制与浅复制

1.潜复制(修改新对象会改变原对象)

var baz = {a:'hello', b: {c:'my', d:'friend'}}
var foo = baz
foo.a="better"
console.log(foo.a)//better
console.log(baz.a)//better

2.深复制(修改新对象不会改变原对象)

var baz = {a:'hello', b: {c:'my', d:'friend'}}
var foo = {}
var deepCopy= function(obj) {
var newObj={};
for (var key in obj) {
      newObj[key] = typeof obj[key]==='object'? deepCopy(obj[key]): obj[key];
   }
   return newObj;
}
foo = deepCopy(obj)
foo.a="better"
console.log(foo.a)//better
console.log(baz.a)//hello

3.对象成环

const isObject = obj => Object.prototype.toString.call(obj) === '[object Object]'

function deepClone(obj, hash = new WeakMap()) {
  if (!isObject(obj)) {
      return obj
  }
  // 查表
  if (hash.has(obj)) return hash.get(obj)

  let isArray = Array.isArray(obj)
  let cloneObj = isArray ? [] : {}
  // 哈希表设值
  hash.set(obj, cloneObj)

  let result = Object.keys(obj).map(key => {
      return {
          [key]: deepClone(obj[key], hash)
      }
  })
  return Object.assign(cloneObj, ...result)
}

验证：

var obj = {};
obj.a = obj; //成环
var o = deepClone(obj);
console.log(o.a === o); // true