SOURCE

function deepClone(obj){//这个方法会有循环引用的问题，比如target.target=target
    let tmp;
    if(typeof obj !='object'){
        return obj;
    }else{
        tmp = Array.isArray(obj) ? []:{}
    }
    for(let key in obj){
        tmp[key] = deepClone(obj[key])
    }
    return tmp;
}

function deepClone(obj){
    let tmp;
    let wp = new WeakMap();
    if(typeof obj !='object'){
        return obj;
    }else{
        tmp = Array.isArray(obj) ? []:{}
    }
    if(wp.get(obj)){
        return wp.get(obj);
    }
    wp.set(obj,tmp);
    for(let key in obj){
        tmp[key] = deepClone(obj[key])
    }
    return tmp;
}
let obj = {
    a:1,
    b:2,
    c:{
        a:[1,2,3],
        b:function(){
            console.log(this.a);
        }
    },
    obj:''
}
//obj.obj =obj
let cpy = deepClone(obj);
//console.log(obj)

console.log(obj.c.b)