Ultra-Easy mobile End layout adaptive size rem Judging js file and exceeding a certain height back to top button code

The following code is placed in a adapt.js file (function  (Doc, win)  {  var docEl =  doc.documentelement,    resizeevt =  ' Orientationchange '  in window  ?  ' orientationchange '  :  ' resize ',     recalc = function   ()  {      var clientWidth = docEl.clientWidth;       if  (!clientwidth)  return;       docel.style.fontsize = 20 *  (clientwidth /750)  +  ' px ';     };   if  (!doc.addeventlistener)  return;  win.addeventlistener ( Resizeevt, recalc, false);   doc.addeventlistener (' domcontentloaded ', recalc,  false);}) (Document, window); Function gotopex ()  { var obj = document.getelementbyid (" Gotopbtn ");  function getscrolltop () &nBsp { return document.documentelement.scrolltop + document.body.scrolltop; }  Function setscrolltop (value)  { if  (DOCUMENT.DOCUMENTELEMENT.SCROLLTOP)  {  Document.documentelement.scrolltop = value; } else { document.body.scrolltop  = value; } } window.onscroll = function ()  { getScrollTop ()   > 0 ? obj.style.display =  "": obj.style.display =  "none";  }  obj.onclick = function ()  { var gotop = setinterval (scrollMove,   function scrollmove ()  { setscrolltop (Getscrolltop ()  / 1.1); if  ( Getscrolltop ()  < 1)  clearinterval (gotop);  } } }

HTML Document code:

<script src= "Js/adapt.js" ></script><--the following is more than the height shown back to the top of the code--><div id= "gotopbtn" ></div> <script Type=text/javascript>gotopex ();</script>

Ultra-Easy mobile End layout adaptive size rem Judging js file and exceeding a certain height back to top button code