js 判断user agent

var UserAgent = 
{
    useragent:window.navigator.userAgent.toLowerCase(),
    android:function()
    {
        alert(this.useragent.indexOf("android"));
        return (this.useragent.indexOf("android") >=0);
    },
    iphone:function()
    {
        return (this.useragent.indexOf("iphone") >=0);
    },
    ipad:function()
    {
        return (this.useragent.indexOf("ipad") >=0);
    },
    mobile:function()
    {
    　　return (this.useragent.indexOf("andriod") >=0) || (this.useragent.indexOf("iphone") >=0) || (this.useragent.indexOf("ipad") >=0);
    }
}