I would imagine your doSomething JS function will fail and produce an error in the logging console because doSomething is probably not expecting to receive an u

I would imagine your doSomething JS function will fail and produce an error in the logging console because doSomething is probably not expecting to receive an undefined. Unless you've written it to handle that scenario and fail gracefully which is probably a good thing to do anyway. Your whole example is silly. Stuff like this is why you write your PHP/JS/Python/Ruby code in a tool like WebStorm/PyCharm/RubyMine which does enough code analysis to realise you've made a typo and flag it.