js 获取页面窗口的大小

var pageWidth = window.innerWidth,               pageHeight = window.innerHeight;       if (typeof pageWidth != "number"){           if (document.compatMode == "CSS1Compat"){               pageWidth = document.documentElement.clientWidth;               pageHeight = document.documentElement.clientHeight;           } else {               pageWidth = document.body.clientWidth;               pageHeight = document.body.clientHeight;           }       }