When using "Show preview" on a page with a graph, a blank space is shown in the space where the graph should be. An error also shows up: "TypeError: Cannot read property 'svg' of undefined" or "ReferenceError: d3 is not defined".
To reproduce: Go to https://www.mediawiki.org/w/index.php?title=Extension:Graph/Demo&action=edit and press "Show preview".
Alternative repo (good for local dev): navigate to Special:GraphSandbox and if four-panel view loads ok and the text editor initializes, copy/paste sample code to it. You might need to add "version": 2 at the top.
Proposed patch partially fixes it, but its not fully initializing yet.