Typescript optional keys reference

The problem: Scenarios where optional keys are needed

Consider this UserRecord:

type UserInfo = 'name' | 'email' | 'age'
type UserRecord = Record<UserInfo, string | number>

This definition makes UserRecord a type where all the keys (name, email, and age) are required.

So this won’t work:

const partialUser: OptionalUserRecord = {
  name: "John Doe" // 'email' and 'age' are optional
}

TypeScript complains with:

But what if we need a UserRecord where some keys can be optional?

The solution: Mapped types

We can use mapped types:

type UserInfo = 'name' | 'email' | 'age'
type OptionalUserRecord = {
  [K in UserInfo]?: string | number
}

Now, we can do something like:

const partialUser: OptionalUserRecord = {
  name: "John Doe" // 'email' and 'age' are optional
}

And TypeScript is happy: