- `change` - generic event triggered for any change on the link
- `change:source` - triggered when the link changes its source
- `change:target` - triggered when the link changes its target
- `change:attrs` - triggered when the link changes its attributes
- `change:smooth` - triggered when the link toggled interpolation
- `change:manhattan` - triggered when the link toggled orthogonal routing
- `change:vertices` - triggered when the link changes its vertices array
- `change:z` - triggered when the link is moved in the z-level (toFront and toBack)
- `transition:start` - triggered when a transition starts.
- `transition:end` - triggered when a transition ends.

    link.on('change:source', function() { alert('source of the link changed') })