Using the navigator object to detect client's browser

Until one browser remains standing on the web (if ever), browser detection will continue to be part of any good JavaScripter's life. Whether you're gliding a div across the screen or creating an image rollover, it's fundamental that only relevant browsers pick up on your code. In this tutorial we'll probe the navigator object of JavaScript, and show how to use it to perform browser detection, whether the subject is Firefox, Internet Explorer, Opera, etc.

The navigator object

The navigator object was conceived back in the days when Netscape Navigator reined supreme. These days it serves as much as an irony of Netscape's demise as way of probing browser information.

Let's see exactly what these properties reveal of the browser you're currently using:

At a glance

At a glance at the above table, you may be swayed towards turning to the following two properties to do your browser detection bidding:

After all, you are trying to detect a browser's name and version right? However, they both will most likely mislead you. In browsers such as various versions of Netscape and Firefox, these two properties return simply "Netscape" for appName, and 5.0 for appVersion without any further distinction for Firefox and its version, and hence are pretty much useless in the real world. For example, in both Firefox 4.x and Firefox 5.x, these two properties return:

appName: Netscape
appVersion: 5.0 (Windows)

We need to turn to a property that's more thorough in its investigative work if we want more consistency and accuracy, and that turns out to be navigator.userAgent.

Detecting Firefox x.x

UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.13) Gecko/20080311 Firefox/2.0.0.13

UserAgent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:5.0) Gecko/20100101 Firefox/5.0

The detail we're interested in apparently lies at the very end, or Firefox/5.0 for example. Different versions of Firefox will contain a different version number, but the pattern is consistent enough. The part we're interested in occurs after the string "Firefox/", or the exact version number. There are many ways to get to it using either standard String or RegExp methods- I'm opting for the later here:

Basically, I'm capturing just the versonMajor.versionMinor portion of the full version number of Firefox (ie: 2.0.0.13 becomes simply 2.0), and using that as basis to detect the various versions of Firefox. Delving any deeper, and the returned version may no longer be a number but a string (ie: 2.0.0), which makes numeric comparisons cumbersome.

Detecting IE x.x

UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 2.0.50727)

So the part we're interested in lies in the middle, or MSIE 7.0;. If you try a shortcut and use


		parseFloat

on the entire string to get to the 7.0 portion, it won't work. This is due to the way parseFloat works- by returning the first number it encounters, which in this case is 4.0. Once again we need to use either standard String or RegExp methods again to get to the actual version number; below I'm using RegExp as well:

Detecting Opera x.x

Detecting Opera using the navigator object at first appears to be tricky business due to the browser's identity crisis. You see, Opera 8 and below by default identifies itself as IE6 (or lower) in the navigator object. Users can override this setting under "Edit Site Settings" in the toolbar to identify as Opera or even another browser instead. Starting in Opera 9, the browser regains its confidence and identifies by default as itself, Opera, though users can still modify this setting manually in the toolbar. The bottom line is, Opera can appear as either Opera, Internet Explorer, or another browser within a designated list in the navigator object.

Lets take a look at what navigator.userAgent in Opera 8.5 returns depending on what it has chosen to identify itself as (whether automatically or manually):

As IE6: Mozilla/4.0 (compatible; MSIE 6.0; Windows XP) Opera 8.5 [en]
As Moz5: Mozilla/5.0 (Windows XP; U) Opera 8.5 [en]
As Opera: Opera/8.5 (Windows XP; U) [en]

Notice how if it's set to identify as IE, MSIE 6.0 appears within the string, while if set to identify as Mozilla,


		Mozilla/5.0

appears instead. As Opera itself, Opera/8.5 appears. In all three cases, the one commonality that we can exploit to actually detect Opera and its true version regardless of which identify it's decided to take on is the string "Opera x.x" or "Opera/x.x" within navigator.userAgent. In other words, there are two versions of the target string we need to be aware of. With that said, here's how you might go about testing for a specific version of Opera, which turns out to be no different than the technique used for detecting, say, Firefox:

Conclusion

We've seen how to use navigator to detect the browser type of your visitors. If the potential pitfalls and complexity of usage of it is a little too much for you, an alternative is to use Object Detection. Whichever method you choose, just be sure to choose one!