Mastering TypeScript Generics for Better Code

TypeScript generics allow you to write code that works with multiple types while maintaining full type safety. They're the foundation of reusable, typesafe utilities.

The Core Mental Model

Think of generics as function parameters for types. Just as a function can accept different values, a generic function or type can work with different types. The type parameter is resolved at the call site, not the definition site.

function identity<T>(value: T): T {
  return value;
}

const str = identity("hello");  // type: string
const num = identity(42);       // type: number

Constraints

Use extends to constrain what types are valid. This lets you access properties that are guaranteed to exist on the type parameter.

Real-World Patterns

The most valuable generic patterns in production code are: generic API response wrappers, generic form field components, generic repository interfaces, and generic event emitters. Once you have these building blocks, you can eliminate enormous amounts of duplicate type definitions.

The Core Mental Model

Constraints

Real-World Patterns

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