回到顶部插件

<script src="jquery-1.11.3.min.js"></script>
<script>
(function($){
    function Obj(element,options){
        this.element = element;
        this.defaults = {
            time:30,
            speed:8,
            scrollTop:100
        };
        this.options = $.extend({},this.defaults,options)
     }
     Obj.prototype.toTop = function(){
          var options = $.extend({},this.defaults,options);
          var timer = null;
          $("body").append($("<span id='toTop' style='position: fixed; 54px;height: 54px;bottom: 50px;right: 70px;cursor: pointer;background: red; z-Index: 101;display:none'></span>"));
          $("#toTop").bind("click",function(){ 
               clearInterval(timer);
               timer = setInterval(function(){
                 var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
                 var iSpeed = Math.floor(0-scrollTop/options.speed);
                 document.documentElement.scrollTop = document.body.scrollTop = scrollTop + iSpeed;
                 if(scrollTop == 0){
                    clearInterval(timer);
                  } 
                    },options.time);
               });
          return this;
     };
     Obj.prototype.scroll = function(){
         var options = $.extend({},this.defaults,options);
         this.element.bind("scroll",function(){
             var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
             if(scrollTop>=options.scrollTop){
                  $("#toTop").fadeIn(); 
              }else{
                  $("#toTop").fadeOut();
              }
         })
         return this;
     }
    $.prototype.extend({
         "toTop":function(options){
            var toTop = new Obj(this,options);
            return toTop.toTop()
         },
         "scroll":function(options){
            var scroll = new Obj(this,options);
            return scroll.scroll()
         }
    })
})(jQuery)

$(function(){
  $("#toTop").toTop({
     time:30,
     speed:8
  });
  $(window).scroll({
    scrollTop:100
  });
})
</script>