Working with APIs and Typed Fetch

fetch itself isn't generic — TypeScript doesn't know what shape an API response has, so you assert or validate it against an interface you define.

interface GitHubUser {
    login: string;
    public_repos: number;
}

async function getUser(username: string): Promise<GitHubUser> {
    const response = await fetch(`https://api.github.com/users/${username}`);
    return response.json() as GitHubUser;
}

Common mistakes

• Treating as GitHubUser as a real runtime guarantee — it only tells the compiler what to assume; it doesn't check the actual response at runtime. For real validation, use a schema library (like Zod) that checks and produces the type together.