TypeScript Return Type For SetTimeout Function

Without actually knowing the return type of setTimeout, we can have TypeScript infer the type by using the utility type ReturnType<Type>.

const timer: ReturnType<typeof setTimeout> = setTimeout(() => {
  console.log('Hello World!') 
}, 1000)

If you then hover over the timer constant, you'll see that it's of type number. In fact, setTimeout returns a numeric id.