TypeScript Tricks I Love

TypeScript has a few utility types that I find myself using in almost every project.

Partial and Pick

Sometimes you only want a subset of a type.

typescript
interface User {
  id: string;
  name: string;
  email: string;
  role: 'admin' | 'user';
}

// Only need id and email for this function
function sendEmail(user: Pick<User, 'id' | 'email'>) {
    console.log(`Sending to ${user.email}`);
}

Advanced Generic Constraints

You can enforce that a generic type must have certain properties.

typescript
function getKey<T extends object, K extends keyof T>(obj: T, key: K) {
    return obj[key];
}

const user = { name: "Sage", age: 30 };
const name = getKey(user, "name"); // Valid
// const fail = getKey(user, "address"); // Error: Argument of type '"address"' is not assignable...