Change events

Yes, there are even more events to tap into. With a ‘change’ event can listen to the changes of any property.

And when you’re animating that property you will get 🔃 continuous updates of the changes. (list of animatable properties in Animation)

For example, if you were to listen to a layer’s rotation…

# print the rotation value
layer.on "change:rotation", ->
    print this.rotation

…you would see a stream of values appear in the Console when a rotation animation is running.

Note that for all the other events we’ve been using shortcuts.

This:

layerA.onTap ->

Is short for this:

layerA.on Events.Tap, ->

Change events don’t have shortcuts, so you must always write the , before the ->.

Example change events

Below are some change events that you might not have thought of.

You can look at the position or size of a layer, or both at the same time:

You can also track when the HTML or style of a layer changed, when a child is added or removed from its parent, or when a layer becomes or ceases to be the parent of another layer. And there’s an event specifically for PageComponents.