Accidental PromiseLike

PromiseLikeAdverb.ts

interface PrintAdverb<T> {
  then: <TResult1>(o: ((value: T) => PrintAdverb<TResult1>)) => PrintAdverb<TResult1>;
  absolutely?: string;
  positively?: string;
  veryvery?: string;
  necessary?: string;
}
const pa: PrintAdverb<string> = {
  then: <TResult1>(o: ((value: string) => PrintAdverb<TResult1>)) => o('3')
}
Promise.resolve(pa)
  .then(
    // printer is a string because `Promise`
    // thought it was a `PromiseLike` and
    // 'unwrapped' it by calling then
    (printer: string) => {
      console.log('log flume');
    }
  )