lazy_promise

lazy_promise.ts

class LazyPromise extends Promise {
  constructor(executor) {
    super(executor);
    if (typeof executor !== 'function') {
      throw new TypeError(`executor is not a function`);
    }
    this._executor = executor;
  }
  then() {
    this.promise = this.promise || new Promise(this._executor);
    return this.promise.then.apply(this.promise, arguments);
  }
}