intermezzo.js

Goals

• Schedule events on a virtual timeline
• Play, pause, and seek the timeline
• Minimal performance impact to UI thread
• Works in browsers that support performance.now() (IE10+ and modern Chrome, FF, Edge, and Safari)

What it does

• Schedule callbacks when events on the timeline begin and end
• Compute timing in a Worker to minimize the amount of work that is done on the UI thread
• Correct for setTimeout drift during playback

What it doesn't do

• Animation and tweening
• Update the UI (you should use requestAnimationFrame to repeatedly check the playback state if you want to perform your own actions during playback)
• Render to a Canvas

Why intermezzo.js?

intermezzo.js provides a simple way for you to create a timeline of arbitrary "events" and perform actions when those events begin or end. It makes no assumptions about the purpose of those events (you have to specify your own callbacks).

Usage and examples

Create a new instance of Intermezzo:

You may create multiple instances of Intermezzo within the same page. Instances operate independently of each other, and each instance creates its own Worker thread.

var intermezzo = new Intermezzo()

Add an event to the timeline:

Add an event to the timeline with the specified time and duration. If included, function callback is called when the event begins or ends during timeline playback. The event's unique ID (within this particular instance of Intermezzo) is returned.

var eventId = intermezzo.addEvent(time, duration, callback)

Remove an event from the timeline:

Remove an existing event from the timeline by passing the ID returned from addEvent.

intermezzo.removeEvent(eventId)

Begin playback:

Start playing back the timeline. Playback can only begin if the duration is greater than 0ms (calling play on an instance of Intermezzo with no events will have no effect).

intermezzo.play()

Pause playback:

Pause the playback. Has no effect if playback is already paused.

intermezzo.pause()

Seek to a time in milliseconds:

Seek the timeline to a specific time in milliseconds. Has no effect if playback is in progress (you must pause playback before seeking).

intermezzo.seek(time)

Register a callback:

Fire a callback when one of the following things occurs (use one of these for the value of type):

• begin: a timeline event has begun
• end: a timeline event has ended
• play: playback began
• pause: playback paused
• stop: playback stopped at the end of the timeline
• seek: finished seeking to a new time

The registered callback will fire whenever an event of that type occurs.

intermezzo.registerCallback(type, callback)

Unregister a previously-added callback:

intermezzo.unregisterCallback(type, callback)