FileReader’s loadstart event is now fired asynchronously


Categories: DOM

Releases: Firefox 79


Previously, a FileReader instance’s loadstart event was fired synchronously when a file read operation started. This behaviour didn’t match the File API spec or other browsers, so Firefox 79 has made it asynchronous.

Still, there is a spec issue to consider dispatching the event synchronously as with XMLHttpRequest’s loadstart. We’ll update this note if the change is reverted.