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← All coursesTypeScript: What the Type System Checks6 levels · 27 lessons

A clean build does not mean every line was checked~7 min
Literal types & widening~6 min
The satisfies operator~6 min
Structural typing & excess property checks~8 min
Type Foundations · Review~5 min

any, unknown, and the assertion escape hatch~7 min
Type guards~6 min
Discriminated unions~7 min
Exhaustiveness & never~6 min
any, unknown & Narrowing · Review~5 min

Generics that earn the brackets~7 min
Where inference comes from~7 min
Utility types~7 min
Generics · Review~5 min

Template literal types~7 min
Conditional types~7 min
Mapped types & key remapping~7 min
The infer keyword~7 min
Type Transformation · Review~5 min

What survives to runtime~7 min
Type-only imports & emit~7 min
Module resolution~7 min
Modules & Emit · Review~5 min

Declaration files~7 min
Declaration merging~6 min
What TypeScript 7 changed in tsconfig~7 min
Declaration Files & TypeScript 7 Config · Review~5 min

Course

TypeScript: What the Type System Checks

Know which lines tsc checked, which it accepted without a check, and what TypeScript 7 changed in tsconfig.

Start free: A clean build does not mean every line was checked

The levels

Level I · 5 lessonsType Foundations