深拷贝

function deepClone(target,cache = new Map()){
  if(cache.get(target)){
      return cache.get(target)
  }
  if(target instanceof Object){
      let dist ;
      if(target instanceof Array){
        // 拷贝数组
        dist = [];
      }else if(target instanceof Function){
        // 拷贝函数
        dist = function () {
          return target.call(this, ...arguments);
        };
      }else if(target instanceof RegExp){
        // 拷贝正则表达式
       dist = new RegExp(target.source,target.flags);
      }else if(target instanceof Date){
          dist = new Date(target);
      }else{
        // 拷贝普通对象
        dist = {};
      }
      // 将属性和拷贝后的值作为一个map
      cache.set(target, dist);
      for(let key in target){
          // 过滤掉原型身上的属性
        if (target.hasOwnProperty(key)) {
            dist[key] = deepClone(target[key], cache);
        }
      }
      return dist;
  }else{
      return target;
  }
}