JS Mushroom Episode 2 - Promises (2018-02-23)

js-mushroom-episode-2-promises.js

// Using resolved promises with the .then callback.
Promise.resolve('hello world').then((message) => {
  console.log(message); // Logs "hello world" in the console.
});

// Using rejected promises with the .catch callback.
Promise.reject('error message').catch((err) => {
  console.error(err); // Logs "error message" in the console.
});

// Using resolved promises with async await inside an IIFE (Immediately Invoked Function Expression).
(async () => {
  const message = await Promise.resolve('hello world');
  console.log(message); // Logs "hello world" in the console.
})();

// Using rejected promises with async await.
(async () => {
  try {
    await Promise.reject('error message');
  } catch (err) {
    console.error(err); // Logs "error message" in the console.
  }
})();

// Making your own resolved promises
const resolvingPromise = () => {
  return new Promise((resolve, reject) => {
    resolve('hello world');
  });
};

// Making your own rejected promise.
const rejectingPromise = () => {
  return new Promise((resolve, reject) => {
    reject('error message');
  });
};

// Waiting for many resolved promises with Promise.all
(async () => {
  const promise1 = Promise.resolve('hello world 1');
  const promise2 = Promise.resolve('hello world 2');
  const promises = [promise1, promise2];
  const messages = await Promise.all(promises);
  const message1 = messages[0];
  const message2 = messages[1];
  console.log(message1); // Logs "hello world 1" in the console.
  console.log(message2); // Logs "hello world 2" in the console.
})();

// Handling a rejected promise with Promise.all
(async () => {
  try {
    const promise1 = Promise.reject('error message 1');
    const promise2 = Promise.reject('error message 2');
    const promises = [promise1, promise2];
    await Promise.all(promises);
  } catch (err) {
    console.error(err); // Logs "error message 1" in the console.
  }
})();