TypeScript 3つのType guard 備忘録

個人用備忘録です

typeof

function toUpperCase(x: string | number) {
 if (typeof x === 'string') {
   return x.toUpperCase();
 }
 return '';
}

in

type Enginner = {
  name:string;
  role: string;
}
type Blogger = {
  name:string;
  follower: string;
}
type EngineerBlogger = Engineer & Blogger;

function describeProfile(nomadWorker: EngineerBlogger) {
  console.log(nomadWorker.name);
  if ('role' in nomadWorker) {
    console.log(nomadWorker.role);
  }
  if ('follower' in nomadWorker) {
    console.log(nomadWorker.follower);
  }
}

instanceof

Class Dog {
  speak() {
    console.log('bwbw')
  }
}
Class Bird {
  speak() {
    console.log('fuwagifu')
  }
  fly() {
    console.log('fly')
  }
}
function havePet() {
  pet.speak();
  if (pet instanceof Bird) {
    pet.fly();
  }
}
havePet(new Bird());