React: lazyLoad Throws Exception "Widget container not found for id:"

[timdoherty]

Subject of the issue

The React example code throws an exception whenever lazyLoad is true, whether in GridStackOptions or GridNode.

Your environment

• version of gridstack.js - 11.5.1 but also confirmed in 12.4.0 by cloning the repo and running the React example.
• which browser/OS - Chromium 142, macOS 15.6.1 (24G90)

Steps to reproduce

• clone the gridstack.js repo
• set lazyLoad: true in demo.tsx gridOptions
• start the app with yarn:start
• look for the following exceptions in the console

Investigation

• getWidgetContainer is called by GridStackRender before renderCBFn is ever called.
• Both gridWidgetContainersMap and widgetContainersRef are empty.
• widgetContainer is always null
• A fatal exception is thrown

Expected behavior

The grid should render normally, and content outside the visible view port should lazy load.