How Can I Track Progress in XMLHttpRequest?

Tracking Progress in XMLHttpRequest

Tracking the progress of an XMLHttpRequest can be invaluable for providing visual cues to users, such as progress bars. While the standard API does not explicitly support progress monitoring, there are non-standard extensions that can provide this functionality.

Uploaded Bytes

Monitoring uploaded bytes is straightforward using the xhr.upload.onprogress event. The browser maintains information on the uploaded data size relative to the total file size. This information can be used to calculate the upload progress.

Downloaded Bytes

Tracking downloaded bytes is more challenging, as the browser is unaware of the total size of the incoming data. However, adding a Content-Length header to the server script can provide this information. The header should specify the size of the response body.

With the total size available, the browser can report the received bytes during the download. This progress information can be accessed via the onprogress event handler.

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