返回网页头部

//** jQuery Scroll to Top Control script- (c) Dynamic Drive DHTML code library: http://www.dynamicdrive.com/.
//** Available/ usage terms at http://www.dynamicdrive.com/ (March 30th, 09')
//** v1.1 (April 7th, 09'):
//** 1) Adds ability to scroll to an absolute position (from top of page) or specific element on the page instead.
//** 2) Fixes scroll animation not working in Opera.

var scrolltotop={
 //startline: Integer. Number of pixels from top of doc scrollbar is scrolled before showing control
 //scrollto: Keyword (Integer, or "Scroll_to_Element_ID"). How far to scroll document up when control is clicked on (0=top).
 setting: {startline:100, scrollto: 0, scrollduration:1000, fadeduration:[500, 100]},
 controlHTML: '<img src="../imn/2009/up.png" style="width:24px; height:24px" />', //HTML for control, which is auto wrapped in DIV w/ ID="topcontrol"
 controlattrs: {offsetx:5, offsety:5}, //offset of control relative to right/ bottom of window corner
 anchorkeyword: '#top', //Enter href value of HTML anchors on the page that should also act as "Scroll Up" links

 state: {isvisible:false, shouldvisible:false},

 scrollup:function(){
  if (!this.cssfixedsupport) //if control is positioned using JavaScript
   this.$control.css({opacity:0}) //hide control immediately after clicking it
  var dest=isNaN(this.setting.scrollto)? this.setting.scrollto : parseInt(this.setting.scrollto)
  if (typeof dest=="string" && jQuery('#'+dest).length==1) //check element set by string exists
   dest=jQuery('#'+dest).offset().top
  else
   dest=0
  this.$body.animate({scrollTop: dest}, this.setting.scrollduration);
 },

 keepfixed:function(){
  var $window=jQuery(window)
  var controlx=$window.scrollLeft() + $window.width() - this.$control.width() - this.controlattrs.offsetx
  var controly=$window.scrollTop() + $window.height() - this.$control.height() - this.controlattrs.offsety
  this.$control.css({left:controlx+'px', top:controly+'px'})
 },

 togglecontrol:function(){
  var scrolltop=jQuery(window).scrollTop()
  if (!this.cssfixedsupport)
   this.keepfixed()
  this.state.shouldvisible=(scrolltop>=this.setting.startline)? true : false
  if (this.state.shouldvisible && !this.state.isvisible){
   this.$control.stop().animate({opacity:1}, this.setting.fadeduration[0])
   this.state.isvisible=true
  }
  else if (this.state.shouldvisible==false && this.state.isvisible){
   this.$control.stop().animate({opacity:0}, this.setting.fadeduration[1])
   this.state.isvisible=false
  }
 },
 
 init:function(){
  jQuery(document).ready(function($){
   var mainobj=scrolltotop
   var iebrws=document.all
   mainobj.cssfixedsupport=!iebrws || iebrws && document.compatMode=="CSS1Compat" && window.XMLHttpRequest //not IE or IE7+ browsers in standards mode
   mainobj.$body=(window.opera)? (document.compatMode=="CSS1Compat"? $('html') : $('body')) : $('html,body')
   mainobj.$control=$('<div id="topcontrol">'+mainobj.controlHTML+'</div>')
    .css({position:mainobj.cssfixedsupport? 'fixed' : 'absolute', bottom:mainobj.controlattrs.offsety, right:mainobj.controlattrs.offsetx, opacity:0, cursor:'pointer'})
    .attr({title:'返回头部'})
    .click(function(){mainobj.scrollup(); return false})
    .appendTo('body')
   if (document.all && !window.XMLHttpRequest && mainobj.$control.text()!='') //loose check for IE6 and below, plus whether control contains any text
    mainobj.$control.css({width:mainobj.$control.width()}) //IE6- seems to require an explicit width on a DIV containing text
   mainobj.togglecontrol()
   $('a[href="' + mainobj.anchorkeyword +'"]').click(function(){
    mainobj.scrollup()
    return false
   })
   $(window).bind('scroll resize', function(e){
    mainobj.togglecontrol()
   })
  })
 }
}

scrolltotop.init()