This lesson's interactive features are locked, please to keep using them

Omit Utility Type

The Omit<T, K> utility type is the opposite of Pick<T, K>. It creates a new type by excluding a set of properties from an existing type. I find this one to be very useful when removing sensitive or unnecessary properties from a type. For example, maybe you need to remove a password field from a user object before responding to an API request.

interface DatabaseUser {
  id: string;
  username: string;
  email: string;
  passwordHash: string;
  createdAt: Date;
  updatedAt: Date;
}

// Create a safe user representation without sensitive data
type PublicUser = Omit<DatabaseUser, "passwordHash" | "updatedAt">;

function getUserProfile(userId: string): PublicUser {
  // Fetch user from database...
  const dbUser: DatabaseUser = {
    id: userId,
    username: "johndoe",
    email: "[email protected]",
    passwordHash: "$2a$12$...",
    createdAt: new Date("2023-01-15"),
    updatedAt: new Date()
  };

  // Convert to PublicUser (explicit conversion for clarity)
  const publicUser: PublicUser = {
    id: dbUser.id,
    username: dbUser.username,
    email: dbUser.email,
    createdAt: dbUser.createdAt

    // TSC error:
    // Object literal may only specify known properties, and 'passwordHash' does not exist in type 'PublicUser'.
    passwordHash: dbUser.passwordHash,
  };

  return publicUser;
}

Assignment

Fix the bug in the UserWithoutID type by omitting the id property.