promise_implementation

function PromisePolyfill(executor) {
  let onResolve, onReject;
  let fulfilled = false,
    rejected = false,
    called = false,
    value;

  function resolve(v) {
    fulfilled = true;
    value = v;
    if (typeof onResolve === "function") {
      onResolve(value);
      called = true;
    }
  }

  function reject(reason) {
    rejected = true;
    value = reason;
    if (typeof onReject === "function") {
      onReject(value);
      called = true;
    }
  }
  
  this.then = function(callback) {
  	onResolve = callback;
    if (fulfilled && !called) {
    	called = true;
      onResolve(value);
    }
  	return this;
  }
  
  this.catch = function (callback) {
    onReject = callback;
    if (rejected && !called) {
      called = true;
      onReject(value);
    }
    return this;
  };
  
  try {
    executor(resolve, reject);
  } catch (error) {
    reject(error);
  }
}

PromisePolyfill.resolve = (val) =>
  new PromisePolyFill(function executor(resolve, _reject) {
    resolve(val);
  });

PromisePolyfill.reject = (reason) =>
  new PromisePolyFill(function executor(resolve, reject) {
    reject(reason);
  });

PromisePolyfill.all = (promises) => {
  let fulfilledPromises = [],
    result = [];

  function executor(resolve, reject) {
    promises.forEach((promise, index) =>
      promise
        .then((val) => {
          fulfilledPromises.push(true);
          result[index] = val;

          if (fulfilledPromises.length === promises.length) {
            return resolve(result);
          }
        })
        .catch((error) => {
          return reject(error);
        })
    );
  }
  return new PromisePolyFill(executor);
};

const promise = new PromisePolyfill((resolve, reject) => {
	console.log("Rajat");
	setTimeout(() => reject(42), 100)
})

promise.then(val => console.log(val)).catch(error => console.log(error));