<div id="paper-back">  <nav>   <div class="close"></div>   <a href="#">Home</a>   <a href="#">About Us</a>   <a href="#">Our Work</a>   <a href="#">Contact</a>  </nav> </div> <div id="paper-window">  <div id="paper-front">   <div class="hamburger"><span></span></div>   <div id="container">    <section>     <p>点击左上角的按钮打开菜单</p>     <p>适用浏览器：、FireFox、Chrome、Safari、Opera、傲游、搜狗、世界之窗. <br>不支持IE及以下浏览器。</p>     <p>     <script src="/scripts/bc/_gg__.js" type="text/javascript"></script></p>    </section>    <section></section>   </div>  </div> </div>

var paperMenu = {   $window: $('#paper-window'),   $paperFront: $('#paper-front'),   $hamburger: $('.hamburger'),   offset: ,   pageHeight: $('#paper-front').outerHeight(),   open: function () {    this.$window.addClass('tilt');    this.$hamburger.off('click');    $('#container, .hamburger').on('click', this.close.bind(this));    this.hamburgerFix(true);    // console.log('opening...');   },   close: function () {    this.$window.removeClass('tilt');    $('#container, .hamburger').off('click');    this.$hamburger.on('click', this.open.bind(this));    this.hamburgerFix(false);    // console.log('closing...');   },   updateTransformOrigin: function () {    scrollTop = this.$window.scrollTop();    equation = (scrollTop + this.offset) / this.pageHeight * ;    this.$paperFront.css('transform-origin', 'center ' + equation + '%');   },   hamburgerFix: function (opening) {    if (opening) {     $('.hamburger').css({      position: 'absolute',      top: this.$window.scrollTop() + + 'px'     });    } else {     setTimeout(function () {      $('.hamburger').css({       position: 'fixed',       top: 'px'      });     }, );    }   },   bindEvents: function () {    this.$hamburger.on('click', this.open.bind(this));    $('.close').on('click', this.close.bind(this));    this.$window.on('scroll', this.updateTransformOrigin.bind(this));   },   init: function () {    this.bindEvents();    this.updateTransformOrigin();   }  };  paperMenu.init();