Required<T>

Definition

A built-in utility type that constructs a new type where all properties of the given Type `T` are set to required, removing any `?` modifiers.

Explain Like I'm New

The exact opposite of `Partial`. It looks at a form where everything is optional, and forcefully stamps 'REQUIRED' over every single field.

Real World Example

When a user provides an optional configuration object `ConfigOptions`, but inside your library's core logic, you merge it with defaults to guarantee every setting exists. Your internal functions will type the merged config as `Required<ConfigOptions>`.

Common Use Cases

•Default prop merging
•Strict internal function signatures

Interactive Example

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

const obj1: Props = { a: 5 }; // Valid, 'b' is optional

// We enforce that ALL properties must be present
const obj2: Required<Props> = { a: 5 }; // ERROR: Property 'b' is missing!

const obj3: Required<Props> = { a: 5, b: "hello" }; // Valid!

Interview Questions

basic

What is the opposite of `Partial`?

intermediate

How does `Required` handle properties that were originally typed as `string | undefined`?

Flash Cards

Question

How does it handle string | undefined?

Click to reveal answer

Answer

If a property was optional `age?: number`, `Required` turns it into `age: number`. However, if a property was explicitly typed as `name: string | undefined` (without the `?`), `Required` will NOT remove the `undefined`. It only strips the optional `?` modifier.