RequireAtLeastOne type

RequireAtLeastOne helps create a type where at least one of the properties of an interface (can be any property) is required to exist.

This works because of TypeScript's utility types: https://www.typescriptlang.org/docs/handbook/utility-types.html Let's examine it:

[K in keyof T]-? this property (K) is valid only if it has the same name as any property of T.
Required<Pick<T, K>> makes a new type from T with just the current property in the iteration, and marks it as required
Partial<Pick<T, Exclude<keyof T, K>>> makes a new type with all the properties of T, except from the property K.
& is what unites the type with only one required property from Required<...> with all the optional properties from Partial<...>.
[keyof T] ensures that only properties of T are allowed.

type RequireAtLeastOne<T> = {
  [K in keyof T]-?: Required<Pick<T, K>> & Partial<Pick<T, Exclude<keyof T, K>>>
}[keyof T]

Additional resources