Beginner to Principal
TypeScript Mastery — Beginner to Principal
From your first annotation to principal-level architecture. The real TypeScript compiler runs inside the page, so Type-check reports the diagnostics tsc actually produces, Emitted JS shows exactly what your code compiles to, and Run executes the JavaScript that survives erasure.
The course
Not loading? Open the course in its own tab. It carries the TypeScript compiler, so the first load is large.
Common questions
Do I need to install TypeScript to take this course?
No. The page carries the real TypeScript compiler and runs it in a worker in your browser. Nothing is installed, nothing is sent anywhere, and there is nothing you can break.
How much of TypeScript does it cover?
All of it: 68 modules covering every one of the 72 modules in the TypeScript Mastery specification, across seven levels — from what TypeScript is, through narrowing, generics and the advanced type system, modules and configuration, declaration files and library authoring, production engineering, and principal-level architecture, review and incidents. The curriculum tab maps each specified module to the lesson covering it, and names the gaps where that coverage is partial.
Is the TypeScript course free?
Yes. Every lesson, the graded exercises and the quiz are free and need no account.
Are the exercises actually graded?
Yes. Your code is executed against 343 assertions — some shown, some hidden and aimed at edge cases. The tests check behaviour, never the text of your code, so any correct solution passes.
Are the compiler errors real?
Yes. The Type-check button runs the real TypeScript compiler in strict mode and shows genuine TS-coded diagnostics, not paraphrases, and Emitted JS shows the exact JavaScript your code compiles to. Type-invalid code still runs with its JavaScript meaning, which is itself the lesson about erasure.