how to listen the components change in a component.

I couldn't get this to work either. Error reading components() when setting the listenTo. The tag is empty (no contents inside) on init, so this makes sense.

never mind... i was doing this in the init of the model instead of the view.

init() {
  const children = this.model.components();
  this.listenTo(children, 'add remove', this.handleComponentsChange);
},

this worked after I put it in the correct init :)

The components collection doesn't change, that's why there's no event triggered.

The storage backend is a Backbone collection, see here. You have to listen to its events, specifically add and remove.

As already mentioned by Andreas, you have to add a listener to the collection.

init() {
  const children = this.model.components();
  this.listenTo(children, 'add remove', this.handleComponentsChange);
},