We’ve all been there: that bit of JavaScript functionality that started out as just a handful of lines grows to a dozen, then two dozen, then more. Along the way, a function picks up a few more arguments; a conditional picks up a few more conditions. And then one day, the bug report comes in: something’s broken, and it’s up to us to untangle the mess.

Functions should always have a return value. Not just "get"-like functions, but also (perhaps even more important) the "set"-like functions. Scripts may not use this return value in many cases (ie. it's out of their scope to do anything about it), but in more advanced structures or test suites, the return value of a "set" function is very important (ie. "don't load X if Y was not set", or "Did the function correctly refuse to do X in scenario Y").