js判断当前页面是pc、平板还是手机

		var os = function (){
            var ua = navigator.userAgent,
            isWindowsPhone = /(?:Windows Phone)/.test(ua),
            isSymbian = /(?:SymbianOS)/.test(ua) || isWindowsPhone,
            isAndroid = /(?:Android)/.test(ua),
            isFireFox = /(?:Firefox)/.test(ua),
            isChrome = /(?:Chrome|CriOS)/.test(ua),
            isTablet = /(?:iPad|PlayBook)/.test(ua) || (isAndroid && !/(?:Mobile)/.test(ua)) || (isFireFox && /(?:Tablet)/.test(ua)),
            isPhone = /(?:iPhone)/.test(ua) && !isTablet,
            isPc = !isPhone && !isAndroid && !isSymbian;
            return {
                isTablet: isTablet,
                isPhone: isPhone,
                isAndroid: isAndroid,
                isPc: isPc
            };	
        }();
        if (os.isAndroid || os.isPhone) {   
        	// 手机
            document.write('')
        } else if (os.isTablet) {
        	// 平板
            document.write('')
        } else if (os.isPc) {
        	// pc
            document.write('')
        }