Generics

Generics allow you to write flexible, reusable components that work with a variety of types rather than a single one — without sacrificing type safety. They are one of TypeScript's most powerful features and are used extensively in libraries, frameworks, and everyday application code.

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Why Generics?

Without generics, you would have to choose between writing type-safe code that only works with one type, or using any and losing type safety entirely:

// Too restrictive — only works with numbers
function firstNumber(arr: number[]): number {
  return arr[0];
}

// Too loose — no type safety
function firstAny(arr: any[]): any {
  return arr[0];
}

// Just right — generic
function first<T>(arr: T[]): T {
  return arr[0];
}

const name = first(['Alice', 'Bob']);  // string
const num = first([1, 2, 3]);         // number

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Generic Functions

Declare a type parameter in angle brackets before the parameter list:

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

// TypeScript infers T from the argument:
const str = identity('hello');   // string
const num = identity(42);       // number

// Or specify explicitly:
const bool = identity<boolean>(true);

You can use multiple type parameters: