Warn early if event listener is not a function

[gaearon]

We used to throw if event listener is not a function in Stack:

ReactDOM.render(
  <h1 onClick={{}}>Hello World!</h1>,
  document.getElementById('container')
);

Fiber silently ignores this.

I think we should throw. This would let us add support for objects (e.g. for passive listener configuration) if we want to in a minor rather than a major.

[aweary]

I'll take this one 😀

[gaearon]

You got it!

[aweary]

@gaearon so it looks like Fiber will throw the same error, but it does so lazily. Once you try to click the element it will trigger that invariant. The invariant currently lives in EventPluginHub.getListener, so we could just move it somewhere else like ReactDOMFiberComponent so we throw early?

[gaearon]

I would prefer that.

[gaearon]

It's worth double checking with @sebmarkbage if this was intentional.

[sebmarkbage]

This was indeed intentional. We could warn early, but not throw. Because we should be able to lazily deal with event listeners by only looking at the properties when an event is triggered. Currently we loop over them all but this is an optimizable path.

[gaearon]

Warning early sounds sensible then.

[flarnie]

Hi - just wondering what the status is on this.

[aweary]

@flarnie great timing, I just opened #10453 😄