Bug: onLoadStart is not passed to img

Although it seem a valid event, and it works using vanilla HTML/JS (at least Firefox, Chrome still have an open bug https://bugs.chromium.org/p/chromium/issues/detail?id=458851), it seems that using and onLoadStart event on an img is not working in react.

React version: 17.0.0

Steps To Reproduce

1. With Firefox open browser development tools
2. Disable browser’s cache
3. Using Firefox go to https://ukpcn.csb.app/
4. Check the console

Link to code example: https://codesandbox.io/s/onloadstart-issue-ukpcn

The current behavior

The console shown:

Vanilla img loading
Vanilla img loaded
React img loaded

Seems that the onLoadStart is not working.

The expected behavior

The onLoadStart function should be executed, so logging also React img loading

[keul]

My understanding of the issues:

• the onloadstart event is valid event for images in the specs: https://developer.mozilla.org/en-US/docs/Web/API/GlobalEventHandlers/onloadstart
• It’s true is not supported by Chrome, but this is registered as a bug. The facts that chrome had this issue will make the feature unusable on most of the users, but still…

I’m not sure why React should handle this differently from what the browser is doing.

[sami616]

This seems like something that will need to be fixed for triggering suspense boundaries for images using the loading='lazy' attribute.