Showing a file upload progress bar
Uploading files from the web browser to the server is a rather common feature of modern web applications. Any number of CMS or publishing systems allows users to upload images to include these with their textual content, as shown in the following image:
Here is an example of a web upload in progress. The basic idea behind one of the algorithms to implement the progress bar is to initiate a POST request in an IFrame and then poll some well-known URL for the progress counter. Modern browsers allow us to get the progress information right on the client's side; this is a part of XMLHttpRequest Level 2 and was standardized ...
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