JS back to the top of the instance sharing _javascript tips

If you don't say more, see the example

1, HTML structure

<div class= "Return_top" ></div>

2, CSS style

. return_top{ 
  width:50px; 
  height:50px; 
  Background:url (.. /images/lanren.gif) no-repeat Center #FF8D16; 
  position:fixed; 
  right:30px; 
  bottom:30px; 
  Display:none; 
  Cursor:pointer; 
  z-index:99;
}

3, JS effect

<script>
   $ (function () {
    $ (window). Scroll (function () {
      var topdistance=$ (window). scrolltop ();  Gets the height of the mouse moving in the existing state of this window
      if (topdistance>100) {  //If the move height is greater than 100px, the top icon displays only, if the move height is less than or equal to 100, the top icon does not display
        $ ('. Return_top '). FadeIn (a);
      else{
        $ ('. Return_top '). fadeout (a);
      }
    });
    $ ('. Return_top '). On (' click ', Function () {
      $ (' html,body '). Animate ({scrolltop:0},800);///Must be selected with $ (' html,body ') Otherwise no effect
    })
  ;
</script>

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