# DownloadTask.onProgressUpdate(function callback)
Start from base library version 1.4.0. Please remaining backward compatible.
Listens on the download progress change event.
# Parameters
# function callback
The callback function for the download progress change event.
# Parameters
# Object res
| Property | Type | Description |
|---|---|---|
| progress | number | Download progress percentage |
| totalBytesWritten | number | The length of downloaded data, in bytes |
| totalBytesExpectedToWrite | number | The length of data expected to be downloaded, in bytes |