SOURCE

let map = new WeakMap()
function deepClone(obj){
    if(typeof obj !== "object" || obj === null) {
        return obj
    }
    let newObj
    if(obj instanceof Array){
        newObj = []
    }else{
        newObj = {}
    }
    if(map.has(obj)){
        newObj = map.get(obj)
    }else{
        map.set(obj,newObj)
        for(let key in obj){
        if(obj.hasOwnProperty(key))//防止拷贝原型上的属性
            newObj[key] = deepClone(obj[key])
    }
    }
    
    return newObj
}
let obj2
let obj1 = {
    name:"张三",
    age:18,
    backpage:[{name:1},1,2,3,{obj2}]
}
obj2 = {
    obj:obj1
}
let newObj = deepClone(obj1)
console.log(obj1)
console.log(newObj)