The createdCallback
was previously called readyCallback
:
Custom elements have lifecycle callbacks which can be used to set up presentational aspects of a custom element. These are: readyCallback, which is called after a custom element is created; insertedCallback, which is called after a custom element is inserted into a document; and removedCallback, which is called after a custom element is removed from a document
http://www.w3.org/TR/components-intro/#lifecycle-callbacks
This was changed in the following Bug entry: Bug 22564 - [Custom]: Rename readyCallback to createdCallback. Discussion here.
The reason it isn't in the spec was because the bug was resolved in July 2013 and the draft updated in June. Such are the pitfalls of following working drafts!