Partial Utility Type

There are several built-in utility types that transform existing types into new ones. One of the most useful is Partial<T>, which makes all properties of a type optional. For example:

type User = {
  id: string;
  name: string;
  email: string;
};

// Without Partial
function updateUser(
  userId: string,
  userInfo: {
    id?: string;
    name?: string;
    email?: string;
  },
) {
  // ...
}

// With Partial
function updateUser(userId: string, userInfo: Partial<User>) {
  // ...
}

Instead of copy/pasting the type definition, the Partial<T> utility type allows us to generate a new type based on an existing one. That also means if the original is ever updated, the new type created with Partial<T> type will automatically have those changes!

type User = {
  id: string;
  name: string;
  preferences: {
    theme: string;
    notifications: boolean;
  };
};

// same as 'type LooseyGooseyUser = Partial<User>'
type LooseyGooseyUser = {
  id?: string;
  name?: string;
  preferences?: {
    theme: string;
    notifications: boolean;
  };
};