This is the first in a series of technical posts by me about the internals of Selenium WebDriver. If you’re not interested in technical nitty-gritty, then feel free to step away now.
Still here? Excellent.
This means that there was a lot of “congruent code”: code that performed the same function but was implemented in a different way. The natural result of this was there was the possibility for behaviour to diverge between drivers. Worse, it meant that when a bug was found, we had to check it in every browser, and it wasn’t certain that an individual could actually fix the code. After all, not everyone is comfortable writing in all the languages we use on the project, or is au fait with all the technologies. For an Open Source project like Selenium, this is a major problem: we rely on a relatively small core of key developers backed up with a far larger team of individuals submitting small changes and fixes. Anything that makes it harder for us to function effectively as a development community is a Bad Thing.
So, we wanted a way off the island; a mechanism that would make it easy to share code between the various drivers and selenium core, that allowed us to fix a bug in one place only and have that fix ripple out to every driver that made use of this mechanism. More importantly, it had to be easy to use, and for someone not familiar with a raft of languages and technologies to quickly get started with.
Because this shared code was to be composed of the smallest useful fragments of functionality required for browser automation we decided to refer to them as “Browser Automation Atoms”, or “atoms” for short. Rather than write them from scratch, the easiest thing to do was to extract them from the existing code — this is stuff that’s been battle-tested, so we know it’s robust.
It would also be nice to break the code up into manageably-sized modules, rather than being in a single, monolithic file, which implies some clever “module loading” capability. Except this code isn’t always going to be executing inside an environment where writing “script” tags to load additional scripts is possible. You can’t do that in the guts of a firefox extension, though you can load files other ways. However we tie modules together will need to cope with that.
Ah! These opposing requirements: small modules containing the functions we want to use, no extraneous code, and for everything to be in a single file in order to minimize the pain of loading additional modules. That doesn’t sound like a very compatible list. How we resolved those differences is the topic of my next post….