Question: core vs through2

They do the same thing. He prefers through2 because it's more terse. But don't use the core stream, because sooner or later it will blow up because of different NodeJS versions.

He highly recommends using userland packages whenever possible to shield yourself from NodeJS version changes breaking your app.

Question: how do you close a stream?

Pause mode vs flow mode streams : he well talk about these later. This will answer this. There are ways to destroy streams, if they provide one, but usually it's not required.