TypeScript Required Utility Type

📝 Table Of Contents

• ☕️ Summary
• ▶️ Code Sandbox Example
• 🛠 How It Works
• 🧠 Quiz Question

☕️ Summary

The Required<Type> TypeScript utility type constructs a new type consisting of all properties of Type set to required. If you're following the TypeScript utility types guide, this is the opposite of Partial ↗

Let's continue with our user updating function that uses Partial<Type> in code sandbox. If you haven't followed the guide from the beginning, go back to Partial ↗

We can make a new function to create a user and the Required type is perfect for this!

▶️ Code Sandbox Example

🛠 How It Works

Since we're making a function that will create a new user, we want to make sure the shape of the data matches the User interface.

// User.tsx

export function createUser(user: Required<User>) {
  return { ...user };
}

When calling the createUser function, again, we must pass in every property or T.S. will warn us.

// App.tsx

const user1 = createUser({
  firstName: "Vitalik",
  lastName: "Buterin",
  age: 27,
  favoriteSongs: [
    "Hold On - Moxura",
    "Pressure - Martin Garrix",
    "Run It Up - Lil Tjay",
  ],
});

const user2 = createUser({
  firstName: "Satoshi",
  lastName: "Nakamoto",
  age: 900,
  favoriteSongs: ["Shape of You - Ed Sheeran"],
});

let user3 = createUser({
  firstName: "Lex",
  lastName: "Fridman",
  age: 33,
  favoriteSongs: [
    "Rolling in the Deep - Adele",
    "All About That Bass - Meghan Trainor",
  ],
});

// updateUser function from  Partial<Type> Tutorial :)
user3 = updateUser(user3, { firstName: "Robot" });

const listOfUsers = [user1, user2, user3];

Required<User> will also make every property of User required even if it is set to optional (e.g.) age?: number

🧠 Quiz Question

Given a type Group with 2 optional properties groupName and members:

// User[] is an array of objects of type User from the interface we created

type Group = {
  groupName?: string;
  members?: User[];
};

If we wanted to define a new type StrictGroup with Required<Group> like this:

type StrictGroup = Required<Group>;

Which of the following is true of StrictGroup?