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fs Module Docs Link

Understanding Error-First Callbacks Link

There’s really only two rules for defining an error-first callback:

• The first argument of the callback is reserved for an error object. If an error occurred, it will be returned by the first err argument.
• The second argument of the callback is reserved for any successful response data. If no error occurred, err will be set to null and any successful data will be returned in the second argument.

Eloquent JavaScript - Async (Chapter 11) Link

You Don’t Know JS - Async Link

You Don’t Know JS - Callbacks Link

You Don’t Know JS - Promises Link

MDN - async/await Link

Understanding Jest Mocks

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What the Heck is the Event Loop Anyway? Link Bookmark Loupe Mock Functions Manual Mocking