How far has the upload progressed (Read Only).
This is a value between zero and one; 0 means nothing is sent yet, 1 means upload complete.
uploadProgress is currently not fully implemented in the Web Player. If used in a Web Player it will report 0.5 during the upload and 1.0 when the upload is complete.
Since all sending of data to the server is done before receiving data, uploadProgress will always be 1.0 when progress is larger than 0.