As I mentioned in my previous comment, onSplice is called on creation and on update. I'm following the pattern set up in the parent class onSplice method, found here: https://github.com/Wikia/app/blob/VID-1308/extensions/VisualEditor/wikia/modules/ve/ce/ve.ce.WikiaMediaCaptionNode.js#L83. Incidentally, the parent class also has properties set before the parent constructor is called https://github.com/Wikia/app/blob/VID-1308/extensions/VisualEditor/wikia/modules/ve/ce/ve.ce.WikiaMediaCaptionNode.js#L22.