cheatsheets/bluebird.md

title	category	layout
bluebird.js	JavaScript libraries	default-ad

Also see the promise cheatsheet and Bluebird.js API (github.com). {:.center.brief-intro}

promise
  .then(okFn, errFn)
  .spread(okFn, errFn) //*
  .catch(errFn)
  .catch(TypeError, errFn) //*
  .finally(fn) //*
  .map(function (e) { ... })
  .each(function (e) { ... })

---

Multiple return values

Use Promise.spread.

.then(function () {
  return [ 'abc', 'def' ];
})
.spread(function (abc, def) {
  ...
});

Multiple promises

Use Promise.join.

Promise.join(
  getPictures(),
  getMessages(),
  getTweets(),
  function (pics, msgs, tweets) {
    return ...;
  }
)

Multiple promises (array)

• Promise.all([p]) - expect all to pass
• Promise.some([p], count) - expect count to pass
• Promise.any([p]) - same as some([p], 1)
• Promise.race([p], count) - use .any instead
• Promise.map([p], fn, options) - supports concurrency

Promise.all([ promise1, promise2 ])
  .then(results => {
    results[0]
    results[1]
  })

// succeeds if one succeeds first
Promise.any(promises)
  .then(results => {
  })

Use Promise.map to "promisify" a list of values.

Promise.map(urls, url => fetch(url))
  .then(...)

Object

Usually it's better to use .join, but whatever.

Promise.props({
  photos: get('photos'),
  posts: get('posts')
})
.then(res => {
  res.photos
  res.posts
})

Chain of promises

Use Promise.try.

function getPhotos() {
  return Promise.try(() => {
    if (err) throw new Error("boo")
    return result
  })
}

getPhotos().then(...)

Using Node-style functions

See Promisification.

var readFile = Promise.promisify(fs.readFile)
var fs = Promise.promisifyAll(require('fs'))

Promise-returning methods

See Promise.method.

User.login = Promise.method((email, password) => {
  if (!valid)
    throw new Error("Email not valid")

  return /* promise */
});

Generators

See Promise.coroutine.

User.login = Promise.coroutine(function* (email, password) {
  let user = yield User.find({email: email}).fetch()
  return user
})

Reference

http://bluebirdjs.com/docs/api-reference.html