promise polyfill

promise polyfill.js

class Prom {
  constructor(promiseCallback) {
    this.state = "pending";
    this.value = undefined;
    this.calledResolve = false;
    this.calledReject = false;
    this.innerResolve = () => {};
    this.innerReject = () => {};
    promiseCallback(this.resolved.bind(this), this.rejected.bind(this));
  }

  resolved(value) {
    this.calledResolve = true;
    this.value = value;
    this.then(this.innerResolve);
    // debugger;
  }

  rejected(value) {
    this.calledReject = true;
    this.value = value;
    this.fail(this.innerReject);
  }

  then(cb) {
    if (this.calledResolve) {
      this.innerResolve(this.value);
      return;
    }
    this.innerResolve = cb;
    return this;
  }

  fail(cb) {
    if (this.calledReject) {
      this.innerReject(this.value);
      return;
    }
    this.innerReject = cb;
    return this;
  }
}

const promise = new Prom((resolve, reject) => {
  setTimeout(() => {
    resolve("We did it!");
  }, 1000);
});

promise.then((response) => {
  console.log(response);
});
promise.then((response) => {
  console.log(response, "ave");
});
promise.fail((error) => {
  console.log(error);
});