javaScript去掉重复的字符

function deleteRepeat(str){
    str="$1$,$2$,$3$,$4$,$5$,$6$,$2$,$3$,$4$,$10$,$55$";
    
    var arr=str.split(",");
    var len=arr.length;
    var tmp="";
    for(var i=0;i<len;i++){
     var s=arr[i];
     if(tmp.indexOf(s)==-1){
      tmp+=s+",";
     }
    }
    alert(tmp);
    }