Is there a way to detect the start of a download in JavaScript?

Question

In our current project we are providing a PDF download that can be customized by the user through an HTML form he submits. It takes several seconds to dynamically generate t

Answer 1

What you want is to be able to detect when the size of the downloaded file changes from 0 to a positive value. As far as I know it is impossible to do that with javascript - you need a plug-in that can access the client's file system.

A recommended work around: Create a session per download. Have the client poll the server about the status of the download. This could be "non existed", "not started", "started", "finished". You need some server's side work to persist and update the status of the download plus an AJAX framework.