Promises Basics

(This is a summary of this blog post)

Here is a real world promise chain:

login().then(getContacts).then(getAttachments).catch(error);

What can you do inside the functions getContacts and getAttachments?

You have 3 options:

1. a function that returns a promise

function getContacts(result) {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      resolve(result + ' get contacts.');
    }, 10);
  })
}

1. a function that returns a single value

function getContacts(result) {
  return result + ' I am doing something sync.';
}

1. a function that throws

function getContacts(result) {
  throw new Error('user logged out!');
}

If you want to run the examples clone my git repo.