Bluebird Promises

Converting nodeback library to Promises

const Promise = require('bluebird'),
      fs = require('fs')

Promise.promisifyAll(fs)

// now you can use promise based methods on 'fs' with the Async suffix
fs.readFileAsync('file.txt').then(contents => {
  console.log(contents)
}).catch(err => {
  console.error('error reading', err)
})

Functional Promises

Example of map:

Promise.resolve([ 1, 2, 3 ]).map(el => {
   return Promise.resolve(el * el) // return some async operation in real world
})

Example of filter:

Promise.resolve([ 1, 2, 3 ]).filter(el => {
  return Promise.resolve(el % 2 === 0) // return some async operation in real world
}).then(console.log)

Example of reduce:

Promise.resolve([ 1, 2, 3 ]).reduce((prev, curr) => {
  return Promise.resolve(prev + curr) // return some async operation in real world
}).then(console.log)

Coroutines (Generators)

const promiseReturningFunction = Promise.coroutine(function* (file) {
  const data = yield fs.readFileAsync(file) // this returns a Promise and resolves to the file contents

  return data.toString().toUpperCase()
})

promiseReturningFunction('file.txt').then(console.log)

Automatic Resource Disposal (Promise.using)

function somethingThatReturnsADisposableResource() {
  return getSomeResourceAsync(...).disposer(resource => {
    resource.dispose()
  })
}

Promise.using(somethingThatReturnsADisposableResource(), resource => {
  // use the resource here, the disposer will automatically close it when Promise.using exits
})

Executing in series

Promise.resolve([1, 2, 3])
  .mapSeries(el => Promise.resolve(el * el)) // in real world, use Promise returning async function
  .then(console.log)