Add RequiredProperties utility type

[Thisen]

Suggestion

🔍 Search Terms

• RequiredProperty
• T & Required<Pick<T, K>>
• RequiredProperties

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

I suggest to add a new utlity type, that makes selected properties required:

type RequiredProperties<T, K extends keyof T> = T & Required<Pick<T, K>>

📃 Motivating Example

This could help in such a sneario:

interface Person {
  id: string;
  name?: string;
  alias?: string;
}
// A single property
type PersonWithRequiredName = RequiredProperties<Person, "name">
const john: PersonWithRequiredName = { id: "123123", name: "john" }
// Will error, name is missing
const alice: PersonWithRequiredName = { id: "234234" }

// Multiple properties
type PersonWithRequiredNameAndAlias = RequiredProperties<Person, "name" | "alias">
const fullJohn: PersonWithRequiredNameAndAlias = { id: "123123", name: "john", alias: "j" }
// Will error, alias is missing
const fullAlice: PersonWithRequiredNameAndAlias = { id: "234234", name: "alice" }

💻 Use Cases

An ideal use case would be as part of type predicates to use with Array.prototype.filter:

interface Person {
  id: string;
  name?: string;
  alias?: string;
}
type PersonWithRequiredName = RequiredProperties<Person, "name">

function hasName(person: Person): person is PersonWithRequiredName {
 return (person as PersonWithRequiredName).name !== undefined;
}
const persons: Person[] = [ ... ]
persons.filter(hasName).sort()

[MartinJohns]

See #39522 (comment):

We've opted to not include utility type aliases in the lib unless they're required for declaration emit purposes.