js显示隐藏的问题

为什么这段代码无效

window.onload=function(){
              var oTiwen=document.getElementById('tiwen');
              var oFl=document.getElementById('fl');
              var oFr=document.getElementById('fr');
              oTiwen.onclick=function(){
               // alert(getStyle(oFl,'display'));
                //alert(getStyle(oFl,'display') == 'block');
                if(getStyle(oFl,'display') == 'block'){
                    oFl.style.display='none';
                    oFr.style.display='block';

                }else{
                    oFl.style.display='block';
                    oFr.style.display='none';
                }
              };
        };
        function getStyle(obj,attr){
          if (obj.currentStyle) {
                  return obj.currentStyle[sttr];
                } else {
                  return getComputedStyle(obj, false)[attr];
                }
        }

---

return obj.currentStyle[attr]; 而非 return obj.currentStyle[sttr];

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