var ua = navigator.userAgent;
var ipad = ua.match(/(iPad).*OS\s([\d_]+)/),
    isIphone = !ipad && ua.match(/(iPhone\sOS)\s([\d_]+)/),
    isAndroid = ua.match(/(Android)\s+([\d.]+)/),
    isMobile = isIphone || isAndroid;
    if(isMobile) {
        location.href = 'http://m.domain.com';
    }else{
        location.href = 'http://www.domain.com';
    }
｝
//or separately judge iphone or android
if(isIphone){
    //code 
else if(isAndroid){
    //code
}else{
    //code
}