Javascript 实现点击跳到页头

function popTopTip(obj,img){
      var objDiv = document.createElement("div");
          objDiv.id = "DivPopTip";
          objDiv.style.cssText = "position:absolute; left:0px; top:0px; border:solid 1px #FBD38D; width:41px; height:20px; z-index:10;";
          objDiv.style.left = (document.documentElement.clientWidth + document.documentElement.scrollLeft - 45).toString() + "px";
          objDiv.style.top = (document.documentElement.clientHeight/2 + document.documentElement.scrollTop).toString() + "px";
          objDiv.onclick = function(){document.documentElement.scrollTop=0;};
      var objIframe = document.createElement("iframe");
          objIframe.style.cssText = "position: absolute;width:100%; z-index:-1; border:0; height:100%; top: 0;left: 0; overflow:hidden";
      var objC = document.createElement("div");
          objC.id = "DivPopDivC";
          objC.style.cursor="pointer";
          
      var objImg = document.createElement("img");
          objImg.src = img;
          objImg.style.border = "0px";

          objC.appendChild(objImg);
          objDiv.appendChild(objIframe);
          objDiv.appendChild(objC);
          
          if(document.getElementById("DivPopTip")!=null)
          {
            obj.replaceChild(objDiv,document.getElementById("DivPopTip"));
          }
          else
          {
            obj.appendChild(objDiv);
          }
}

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