Advanced TypeScript
Staff-engineer-level type system mastery. Recursive types, variance, template literal types, declaration files, module augmentation, and TypeScript performance in large projects.
The infer keyword for pattern-matching type structures, extracting return types, parameter types, promise results, and building advanced type utilities that decompose any type.
Tree types, JSON types, DeepPartial, DeepReadonly, and the depth limits that prevent infinite recursion. How to model recursive data structures in TypeScript's type system.
String manipulation at the type level — route typing, CSS unit types, event name generation, and the intrinsic string types that let TypeScript parse and transform strings during compilation.
The in/out modifiers, why function parameters are contravariant, why return types are covariant, and the variance rules that prevent unsound type assignments.
Type checking without type widening — how satisfies differs from type annotations and as casts, when to use each, and the patterns it unlocks for configuration objects and theme types.
How .d.ts files work, the declare keyword, global augmentation, DefinitelyTyped, and writing type declarations for untyped JavaScript libraries.
Extending third-party types without forking, interface merging rules, module augmentation patterns, and the techniques library authors use to make their types extensible.
Composite projects, build mode, monorepo TypeScript setup, and the configuration that turns 60-second builds into 2-second incremental rebuilds.
Type instantiation limits, avoiding slow types, tracing compilation bottlenecks, and the patterns that keep large codebases compiling in seconds.
10 advanced TypeScript brain-teasers covering infer, template literals, variance, recursive types, and satisfies. Staff-engineer-level type system challenges.