promised stream

gistfile1.js

// backpressure is better modeled with a promised event
var stream

// our data listeners are functions that *may* return a promise
// when the promise resolves, the data has been consumed and the stream may continue
stream.on('data', function(data) {
  // simulate being busy by returning a promise that resolves in 150ms
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      console.log('laggy-stream: ', data)
      resolve()
    }, 150)
  })
})

// a separate stream consumer with no lag
stream.on('data', function(data) {
  console.log('no-delay-stream: ', data)
  // returning null (or a non-promise value signifies we're done with data)
})