Js – deep copy

1. Implementation of Es5

var obj = {
  name: "Zhang".age: 34.info: {
    hobby: ["Football"."Basketball"."Table tennis"]}}function deepClone( resource ){
    let target;
    let type = Object.prototype.toString.call(resource).slice(8, -1);
    if( typeof resource == "object" ){
        target =  type === "Array" ? [] : {};
        for( let key in resource ){
            if( resource.hasOwnProperty( key)){
                if( typeof resource[key] =="object"){
                    target[key] = deepClone( resource[key] )
                }else{ target[key] = resource[key]; }}}}else{
        target = resource;
    }
    return target;
}

var newObj = deepClone(obj)
newObj.info.hobby[0] = "Pool";
console.log(obj,newObj)
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2. Implementation of Es6

// The difference between map and wekMap:
Map keys can be arbitrary values. WekMap keys must be objects
// 2. The key of weakMap is a weak reference. After deleting the key, all references will be garbage collected


// hashMap: Avoid dead recursion when objects reference each other
function deepClone(origin, hashMap = new WeakMap(a)) {

  if ((origin == undefined) | | (typeoforigin ! = ="object")) {
    return origin
  };

  // Check whether the current object has been copied (to avoid an endless loop caused by object references)
  const hashKey = hashMap.get(origin);
  if (hashKey) return hashKey;

  // Create new objects or arrays using the constructor attribute
  const target = new origin.constructor();
  hashMap.set(origin, target);
  for (let k in origin) {
    if(origin.hasOwnProperty(k)) { target[k] = deepClone(origin[k], hashMap); }}return target;
}

var obj1 = {};
var obj2 = {};
obj2.obj1 = obj1;
obj1.obj2 = obj2;

//1. Dead recursion occurs when hashMap is not used
//2. Using the hashMap inner loop only fires twice
deepClone(obj2)
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