I am currently working on creating a file upload progress feature that is compatible with older browsers using AJAX. In HTML5, there is the xhr.upload.progress event which works well for modern browsers, but I need an alternative for non-XHR2 browsers. I have decided to use the APC extension to track the progress.
My main question now is: what is the most effective way to trigger a custom-built xhr.upload.progress event? My initial plan is to utilize HTML5 SSE's, but if they are not supported, I am unsure of the best fallback option.
- Polling: making continuous AJAX requests for progress updates every few seconds
- Long-polling: some say this is better than regular polling, although it can potentially cause the server to become unresponsive since the requests aren't handled asynchronously. To avoid this issue, I might need to consider using NodeJS. If the freezing problem is exaggerated, I may lean towards long-polling.
- Un-ending iframe: using an iframe might be a viable solution, but there could be drawbacks as well. Does it also have a tendency to overload the server like long-polling?
Edit: In addition to my original questions, I am also concerned about scalability with these AJAX methods. Do EventSource SSEs lead to excessive memory usage on the server? If so, would it be wise to explore alternatives like NodeJS or ScaleStack? And finally, does the server workload really matter when it comes to displaying an upload progress bar?