Mastering TypeScript: Interfaces, Generics, Unions Explained

The declaration-merging distinction is the one point here that actually explains why the interface-vs-type-alias debate exists, rather than just listing feature parity. Most explanations stop at "interfaces are for objects, types are for unions," but merging is the concrete case where they genuinely aren't interchangeable, a library augmenting a global interface (like extending Window or a third-party type) needs that behaviour, and no type alias can replicate it.

The type-narrowing section is worth its own follow-up post, honestly, the typeof check example is the simple case, but narrowing gets a lot more interesting (and more useful in practice) once you get into discriminated unions with a shared kind/type field, since that's usually how real API response shapes end up modeled rather than plain string | number.

Really well-structured piece, and worth pointing out from an SEO angle: the way you've broken this into numbered sections with a clear TOC is exactly what tends to earn featured snippets and "jump to section" rich results on Google for technical queries like "typescript generics vs interfaces." Long-form technical docs that skip structure like this usually rank for the title but miss out on ranking for the dozen sub-questions buried inside. Small thing, but it compounds a lot over time for tutorial content like this.

What is your thought on learning the syntax after the AI era?