js判断是否移动端及浏览器内核

var browser = { 
    versions: function() { 
        var u = navigator.userAgent; 
        return { 
            trident: u.indexOf('Trident') > -1, //IE内核 
            presto: u.indexOf('Presto') > -1, //opera内核 
            webKit: u.indexOf('AppleWebKit') > -1, //苹果、谷歌内核 
            gecko: u.indexOf('Firefox') > -1, //火狐内核Gecko 
            mobile: !!u.match(/AppleWebKit.*Mobile.*/), //是否为移动终端 
            ios: !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/), //ios 
            android: u.indexOf('Android') > -1 || u.indexOf('Linux') > -1, //android 
            iPhone: u.indexOf('iPhone') > -1 , //iPhone 
            iPad: u.indexOf('iPad') > -1, //iPad 
            webApp: u.indexOf('Safari') > -1 //Safari 
        }; 
    }
} 

if (browser.versions.mobile() || browser.versions.ios() || browser.versions.android() || browser.versions.iPhone() || browser.versions.iPad()) { 
    alert('移动端'); 
}