Effective TypeScript is nearly 400 pages long, but I've received the most feedback by far on just one passage. It comes in Item 7: Think of Types as Sets of Values: keyof (A&B) = (keyof A) | (keyof B) keyof (A|B) = (keyof A) & (keyof B) If you can build an intuition for why these equations hold, you'll have come a long way toward understanding TypeScript's type system! I'll explain these equations in a moment. But before I do, head over to the TypeScript Playground and test them out with a fe...
