var oA = document.getElementsByTagName("a");
        var oCon = document.getElementsByClassName("content");
        for(var i = 0;i<oA.length;i++){
            //alert(i)
            oA[i].index = i;
            oA[i].onclick = function(){
                //alert(i)
                for(var j =0 ; j<4;j++){
                    oA[j].className = ""
                    oCon[j].style.display = "none";
                }
                
                this.className = "on";
                //alert(i);
                oCon[this.index].style.display = "block";
            }
        }