Errata

To clarify future editions—and especially, to reinforce the message of Item 14 (Use Type Operations and Generics to Avoid Repeating Yourself)—it would help to replace the Vector1, Vector2, Vector3 example from Item 7 with something else. The book presents type-operational equivalents two pages later in `[number, number]` and `[number, number, number]`; since `x`, `y` and `z` are basically ordered placeholders just like '0', '1', and '2', intuition suggests a similar relationship between the VectorN types and list types (and indeed, some programming languages use the two terms interchangeably). Even sticking to the geometric usage of "Vector", one doesn't typically say a 3d vector "is-a" 2d vector, but that one can project the former to the latter. While it's all still correct by the rules of TS, an example with less conceptual baggage would reduce the opportunity for confusion.

And thank you for your work creating Effective TypeScript. I would not mention the above issue, were it not for the overall superb quality of the book—evidence you all care a great deal that the writing be clear as possible.