# Generic Functions — TypeScript

Source: https://www.geekswithgeeks.com/en/typescript/ts-generic-functions

> Write one function that works with many types, safely.

## A generic identity function

`<T>` is a type placeholder, filled in by whatever type is actually passed — unlike `any`, the relationship between input and output stays type-safe.

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

const a = identity<number>(42);      // a: number
const b = identity("hello");         // b: string, T inferred
```

## A labeled box

Think of `T` as a **labeled shipping box** — you don't know what's inside until it's packed, but whatever goes in comes out the same, unchanged.

## A generic array helper

The same generic function works with arrays of numbers, strings, or objects — TS keeps every call type-checked.

```typescript
function firstElement<T>(arr: T[]): T | undefined {
  return arr[0];
}

firstElement([1, 2, 3]);          // number | undefined
firstElement(["a", "b"]);         // string | undefined
```