simulate-photos.js

const event_emitter = require('events');

class PhotoAnalyzer extends event_emitter {
  constructor() {
    super();
    this.times =
      new Array(10).fill(undefined).map(() => Math.floor(Math.random() * 10000));
  }
};

const download = new PhotoAnalyzer;

download.on('download-piece-complete', function(part_index) {
  console.log(this.times[part_index]);
});

Promise.all(
  download.times.map((delay, i) => {
    return (new Promise(accept => {
      setTimeout(() => accept(i), delay);
    })).then(spot => download.emit('download-piece-complete', spot));
  })
);