UploadOnBeforeUploadEvent

The onBeforeUpload event.

Name	Type	Default	Description
additionalData	UploadAdditionalData		The additional data that will be sent with the request. Can be modified.
files	UploadFileInfo[]		The files that will be sent with the request.
headers	UploadHttpHeaders		The headers that will be sent with the request. Can be modified.
target	any		An event target.