typescript-advanced-types

Define an event map type mapping event names to payload types, then use generics with mapped types to type the on and emit methods. The compiler enforces that emitted data matches the declared payload for each event name.

Use conditional types with the infer keyword, such as T extends (...args: infer P) => infer R. TypeScript also provides built-in ReturnType and Parameters utility types for common extraction cases.

Mapped types iterate over an existing type's properties to transform them, like Partial or Readonly. Conditional types select a type based on a condition using extends, enabling logic like extracting types or distributing over unions.

Use unknown for values whose type is not yet determined, since it forces type narrowing through guards before use. Unlike any, unknown preserves type safety and prevents accidental operations on unchecked values.

Each conditional branch forces the compiler to evaluate type relationships recursively, and deeply nested or recursive types multiply this work exponentially. Cache complex type computations in named aliases and limit recursion depth to reduce compile times.

Discriminated unions use a shared literal field like status or type so switch statements narrow each branch to the exact variant. This gives full autocomplete and compile-time exhaustiveness checking without manual type assertions.