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';

    ｝

    //或者单独判断iphone或android

    if(isIphone){

        //code

    else if(isAndroid){

        //code

    }else{

        //code

    }