javascript原生foreach方法重写

var arr = ['张三','李四','王五','王琦','马六','八路']

  Array.prototype.forEach = function(fun,desc){
	var arrleng = this.length;
	if(desc == 'order'){
	  for(let i = arrleng-1 ; i >= 0; i--){
	  fun(this[i],i,this);
	  }
	}else{
	  for(let i = 0; i < arrleng; ++i){
	  fun(this[i],i,this);
	  }
	}
  }
  arr.forEach((item,index)=>{
   console.log(item);
	},'order')