All Components


Fires when one or more files are about to be uploaded. If you cancel the event, the upload is prevented.

Arguments for the upload event:

data Object

The optional object that is sent to the upload handler in the form of key/value pair.

files Array<FileInfo>

The list of the files that are about to be uploaded.

headers Headers

The headers of the request.



If the event is prevented by any of its subscribers, returns true.


boolean true if the default action was prevented. Otherwise, returns false.


Prevents the default action for a specified event.
In this way, the source component suppresses the built-in behavior that follows the event.

In this article