promises.md

#promises talk for queensjs 4/11/15

• es6 article
• es7 article
• mdn

why do we use them

• js is single threaded
  • you can add listeners to events, but what if the event happens before you start listening for it?
• handling errors becomes really difficult in other async options

what are other async options

• continuation calling style
• callbacks
• communicating..?
• using threads

how do they work

• finally invoked at end no matter how the promise resolves
• Promise.all takes an array of promises and creates a promise that fulfills when all of them successfully complete
  • returned same order as passed in

what are some libraries to use

• native in js es6
• q
• bluebird
• when
• winjs
• rsvpjs
• jquery

what's happening in the future with promises

• es7 has new features

async function myFunction() {
  let result = await somethingThatReturnsAPromise();
  console.log(result); // cool, we have a result
}
// or
async function myFunction() {
  try {
    await somethingThatReturnsAPromise();
  } catch (err) { 
    console.log(err); // oh noes, we got an error
  }
}

• can use them via some libs

  • babel
  • regenerator

• every promise returns a new promise (true?)