Question

I want to add javascript into my template to detect that every time users view my websites with what kind of device (Smartphone, tablet or PC).

Currently, I try to do it with javascript, here it is:

var smartPhone = "smartphone";
var Ipod = "ipod";

var userDevice = navigator.userAgent.toLowerCase();

function DetectPhone()
{
   if (userDevice.search(smartPhone) > -1)
      return true;
   else
      windows.location = "/pageforphone.aspx";
}

function DetectIpod()
{
   if (userDevice.search(Ipod) > -1)
      return true;
   else
      windows.location = "/pageforpod.aspx";
}

Did I write the codes right? Honestly, no iPhone…

Of course, if these were completed with Php or Asp.net would be better, but is it true that people always turn the javascript off on their palm devices?
Also, i think iphone or ipod or any other tablets are quite similar, is it ok that i use same redev pages for those devices? Actually i am not very understanding what is the differences among them and what should i be aware when i redev my web pages.

Answer 1

The premise of the question, that browser-sniffing is acceptable, is false. You should never engage in browser sniffing, simply because you cannot confidently accomplish what you set out to accomplish. User Agent Strings are not immutable, and are often times changed by plugins installed on the client machine, or by the client themselves (not uncommon, since bad programmers may lock them out of a site based on their UA-String).

Rather than asking what device the user is one, you should instead be asking what functionality is the device capable of. This brings you to feature detection, where you set out to do X, test to see if the user agent is capable of doing X, and then proceed to do or not do X. For instance:

if ( !!document.createElement("video").canPlayType ) {
  console.log( "HTML5 Video Supported" );
}

This is more reliable than trying to see if the user is on an iPhone, iPad, Windows Tablet, or HTML5 Enabled Browser. You can use tools like Modernizr to perform a lot of these tests for you – over 40 in fact.