Generics

A generic lets a function or class work with any type, while still keeping full type safety — instead of writing the same logic once per type, or giving up and using any.

Syntax

function firstItem<T>(items: T[]): T {
    return items[0];
}

Example

const firstNumber = firstItem([1, 2, 3]);       // inferred as number
const firstName = firstItem(["Ada", "Grace"]);  // inferred as string

T is a placeholder for "whatever type is actually passed in" — TypeScript infers it from the argument, and the return type automatically matches, giving you both flexibility and safety at once.

Practice

Write a generic function wrapInArray<T>(value: T): T[] that returns a one-element array containing the value.

function wrapInArray<T>(value: T): T[] {
    return [value];
}