If you're building a web app (of more than trivial complexity, where you need to do things like profile for performance or access the user's hardware), you are

If you're building a web app (of more than trivial complexity, where you need to do things like profile for performance or access the user's hardware), you are building four apps: Chrome, IE, Firefox, and Safari. I mean, there are other browsers, but let's not kid ourselves. ;) You are, in fact, also building those four apps on five different architectures: Android, Windows, Mac, Linux, and iOS. There are others, but again, let's not kid ourselves. Your complexity surface is the product of your feature-set, the quirks of each of those browsers as they silently version-up for your users, and the quirks of each of those browsers on each OS platform as they also vary in version. If you're building a trivial web app, it's a web page and by all means build it directly in the browser. But when you start to bust out the profiler to figure out why this one interaction is butter-smooth in Chrome and runs like crap in Firefox from versions X to Y, except on Linux where it's X to Z... Two mobile platforms is fewer than 4 browser platforms.