js如何删除数组中重复的值

Array.prototype.deleteEle=function() 
{ 
  var obj={};
  var newArr=[];
  var i,j; 
  for(i=0;i<this.length;i++) 
  { 
    if(typeof(obj[this[i]])=="undefined") 
    { 
      obj[this[i]]=""; 
    } 
  } 
  for(j in obj) 
  { 
    newArr.push(j) 
  } 
  return newArr; 
} 
var theArray=new Array(1,2,3,4,5,6,8,5,4);
document.write(theArray.deleteEle());