JS simulates multi-threading_javascript skills

var Thread = {
 runNum : 0,  //当前正式运行的线程数
 maxNum : 10, //最大同时执行的线程数 -1表示不限
 commandList : new Array(), 
 start : function(){
  //window.status = this.runNum; 
  if(this.maxNum != -1 && this.runNum >= this.maxNum){   
   return; 
  }
  if(this.commandList.length <= 0){  
   this.runNum = 0;
   return false; 
  }  
  this.runNum ;
  var _this =this;  
  var tFun = function(){
   if(!_this.commandList[0]) return;
   var command = _this.commandList[0].shift();   
   command.apply(_this,_this.commandList[0].concat(
    function(){  //alert(2)     
     if(_this.runNum > 0)_this.runNum--; 
     setTimeout(function(){_this.start.apply(_this)},1);     
    }));
   _this.commandList.shift(); 
  }
  setTimeout(tFun,1);  
  setTimeout(function(){_this.start.apply(_this)},10);
 }
}