At least to me there is no specific method, I work mainly with Java, since your specific case is JavaScript it may not even apply. If the problem is some bug a

At least to me there is no specific method, I work mainly with Java, since your specific case is JavaScript it may not even apply. If the problem is some bug and there are stack traces that is my starting point, debugger and a few breakpoints chosen from the trace and then follow the stack and from there I start knowing how it is structured, and then the next bug and so on (fixing them of course) For code where I need to add features things get a little more tricky, but there is always some entry point, a web-service invocation, some web page, and try to understand what it is currently doing, again using the debugger to follow the calls and how the data is changed (sometimes even going into libraries). Reading the docs if there are any is also a good place to start. Once again, use the debugger a lot, makes it easier to understand than just reading the code. (edit: formatting)