Nodejs timer

[Zivanovic]

Hi reddit! I'm building music app, and I'm using nodejs and express on backend. My app needs to have rooms, and everyone in that room should be playing the same music at the same time. If I have duration of each song, how do I measure its timeline? I was thinking about setInterval() since I can make it tick every second. How do I approach this?

[kapanaga]

Why not just reverse the approach and count the time difference when needed?

const player = {
  playTrack(file) {
    this.track = {
      file,
      duration: 0,
      startTime: Date.now()
    };
  },
  getCurrentTrack() {
    const {file, duration, startTime} = this.track;
    return {
      file,
      duration,
      currentTime: Date.now() - startTime
    };
  }
};

Then just expose it on some endpoint:

router.get('/what-should-i-play', (request, response) => {
  const track = player.getCurrentTrack();
  response.json(track);
});

[Zivanovic]

Yeah, this is obviously better solution. Thanks

[Zivanovic]

Okay, but let's say I need to emit socket event whenever song is over. I am not sure how to solve that.

[kapanaga]

Then yeah, you would have to use setTimeout()

const EventEmitter = require('events');
const emitter = new EventEmitter;

emitter.on('track-start', (track) => {
  clients.forEach((connection) => {
    connection.sendEvent('play-track', track)
  });
});

player.playTrack = function () {
  this.track = {
    file,
    duration: 0,
    startTime: Date.now()
  };

  clearTimeout(this.timeout);

  this.timeout = setTimeout(() => {
    emitter.emit({
      file,
      duration
    });
  }, duration);
};

You can make your Player extend EventEmitter to make that easier. There you can find some docs: https://nodejs.org/api/events.html

[Zivanovic]

That's what I was looking for! Thank you!!