TS - Typescript example of a Predicate Type Guard

example-typescript-predicate-type-guard.ts

export interfac-e NpmContributors {
  email?: string;
  githubUsername?: string;
  name: string;
  url?: string;
}

export interface NpmMaintainer {
  email: string;
  name: string;
}

export const isContributor = (npmType: NpmMaintainer | NpmContributors): npmType is NpmContributors => {
  return (npmType as NpmContributors).url !== undefined;
}