I was expecting more of a 'write your own implementation' kind of thing, but it's not really that. For example, the replacement for _.concat() is really just a

I was expecting more of a 'write your own implementation' kind of thing, but it's not really that. For example, the replacement for _.concat() is really just advice on how to concatenate arrays in-line. In such cases, I think learning that a packaged function is not needed is pretty nifty.