滚动到顶部固定JavaScript代码

/* 侧边栏固定*/
 function menuFixed(id) {
     var obj = document.getElementById(id);
     var _getHeight = obj.offsetTop+10;
     window.onscroll = function() {
         changePos(id, _getHeight)
     }
 }
 function changePos(id, height) {
     var obj = document.getElementById(id);
     var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
     if (scrollTop < height) {
         obj.style.position = 'relative';
       }
      else{
         obj.style.position = 'fixed';
         obj.style.top = 0;
     }
 }
 window.onload = function() {
/* 需要固定的id（#guding）*/
     menuFixed('guding')
 }