In this case it doesn't make a difference whether @types/emojione is a dev dependency or not because the .d.ts will only expose one signature that has only built-in types. But if we would have a function that for example exposes a Buffer as part of one signature and we would need @types/node as a normal dependency since the generated .d.ts file has a connection to it. So the best practice would be to just do it for all dependencies that you actually use during runtime.
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