Simple Promise Implementation

README.md

Simple Promise Implementation

A simple javascript implmentation of promise object. It isn't the best solution but does solve the given problem statement. The probable todo items/improvements would be to refer MDN doc for Promise

Listing a few here:

1. .all(iterable)
2. .reject(promiseInstance)
3. .resolve(promiseInstance)
4. .finally(callback)

promise.js

function MyPromise(callback) {
  var queue = [];
  var catchMe;
  var resolve = function(value) {
    let lastVal = value;
    queue.forEach((next) => {
      lastVal = next(lastVal);
    });
  };
  var reject = function(error) {
    catchMe(error);
  };
  callback(resolve, reject);
  return {
    then: function(cb) {
      if (typeof cb === 'function') queue.push(cb);
      return this;
    },
    catch: function(cb) {
      catchMe = cb;
    },
  };
}

var aPromise = new MyPromise(function(resolve, reject) {
  setTimeout(function() {
    resolve('Accepted');
    // reject('Error');
  }, 1000);
})
.then(function(value) { console.log(value); return value; }) // ‘Accepted’
.then(function(value) { console.log(value) }) // ‘Accepted’
.catch(function(error) { console.log(error) }); // ‘Error’