There's only one way to learn how to write code: Write code.
Don't get me wrong, you still need to read, a lot.
In my experience, the best way to understand what some unfamiliar code does is to copy & paste it into your test environment and run it through a step-by-step debugger, checking out the variables values at every row.
Note that this (and recursion also) doesn't apply only to javascript, but to any programming language.
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There's only one way to learn how to write code: Write code.
Don't get me wrong, you still need to read, a lot.
In my experience, the best way to understand what some unfamiliar code does is to copy & paste it into your test environment and run it through a step-by-step debugger, checking out the variables values at every row.
Note that this (and recursion also) doesn't apply only to javascript, but to any programming language.