Required<Type>

INFO

The Required<Type> utility type is available starting from TypeScript version 2.8. For more information see in TypeScript Handbook, Release Note.

Overview

Required<Type> is a built in utility type in TypeScript that contructs a type with all properties of Type set to required. This is the opposite of Partial<Type>.

Syntax

type Required<T> = { [K in keyof T]-?: T[K] };

• Type (T): The type whose properties you want to make required.

Examples

Exmaple #1

interface Props {
  a?: number;
  b?: string;
}

const obj1: Props = { a: 5 };
const obj2: Required<Props> = { a: 5 };

// Error
// Property 'b' is missing in type '{ a: number; }'
// but required in type 'Required<Props>'

// Required<Props> is equivalent to the following:
// interface Props {
//     a: number;
//     b: string;
// }

Exmaple #2

interface SignUpForm {
  username?: string;
  email?: string;
  password?: string;
  confirmPassword?: string;
}

type RequiredSignUpForm = Required<SignUpForm>;

function validateSignUpForm(signUpData: RequiredSignUpForm): boolean {
  const requiredFields = ['username', 'email', 'password', 'confirmPassword'];

  for (const field of requiredFields) {
    if (signUpData[field as keyof RequiredSignUpForm] == null) {
      console.error(`Field ${field} is missing`);
      return false;
    }
  }

  if (signUpData.password !== signUpData.confirmPassword) {
    console.error(`Passwords do not match`);
    return false;
  }

  return true;
}