判断浏览器

        var browser=navigator.appName;
        if(browser == 'Microsoft Internet Explorer'){
            bg.style.height = Math.max(document.body.scrollHeight,document.body.offsetHeight);
            bg.style.width = Math.max(document.body.scrollWidth,document.body.offsetWidth);
        }else{
            bg.style.width='100%';
            bg.style.height='100%';
        }
        alert(browser);*/
        var Sys = {};
        var ua = navigator.userAgent.toLowerCase();
        if (window.ActiveXObject)
            Sys.ie = ua.match(/msie ([\d.]+)/)[1]
        else if (document.getBoxObjectFor)
            Sys.firefox = ua.match(/firefox\/([\d.]+)/)[1]
        else if (window.MessageEvent && !document.getBoxObjectFor)
            Sys.chrome = ua.match(/chrome\/([\d.]+)/)[1]
        else if (window.opera)
            Sys.opera = ua.match(/opera.([\d.]+)/)[1]
        else if (window.openDatabase)
            Sys.safari = ua.match(/version\/([\d.]+)/)[1];