Using a real DataTransfer object with a drop event fails

• @testing-library/dom version: latest
• Testing Framework and version:
• DOM Environment:

Relevant code or config:

https://github.com/testing-library/dom-testing-library/blob/accb6cc60628cb6b5bd4d9be2ead41724995e5ae/src/events.js#L74 - this assumes it only needs to copy across named properties - But if the caller uses an actual DataTransfer object e.g. by calling new window.DataTransfer() - adding data to it and passing it in, then this won't read the properties off it.

Try it for yourself - in Chrome Object.getOwnPropertyNames(new window.DataTransfer()) returns an empty array.

This means - it's impossible to use a DataTransfer object, add data to it and then use it for the event.

Suggested solution:

if the dataTransfer value passed to the event is an actual instance of window.DataTransfer then just pass it on - don't try to copy properties over to a new instance

Start in src/events.js at the referenced line, where event properties are copied into a new event value. Reproduce the drop-event case with a real DataTransfer object, then verify that its data remains available when the event is dispatched.