// lesson 3 of 12 · 18 min

Typed functions and generics

function describe(course: Course): string {
  return `${course.title} -- $${course.price}`;
}

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

firstItem<string>(["a", "b"]); // T inferred as string

Generics let a function stay type-safe while working across many types — the same idea as generics in Java or C++, adapted to JavaScript's structural type system.

Try it yourself

Exercise: Write a generic firstItem<T> function that returns the first element of an array.

Expected output:

typescript

Output

Run your code and get it working before marking this lesson complete.

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