导出CSV和Javascript并显示进度条

Question

Is there a way to display a progress bar while a CSV file is being generated and served up via ajax? The CSV file takes a while to generate due to the database, and need a loader on the screen and hide it when it is done. I would like this to be ajax or stay on the same page if necessary. Right now I am doing this below, but I can't tell when the file is done downloading to stop the progress.

var iframe = document.createElement("iframe");
                iframe.src = (value.url);
                iframe.style.display = "none";
                document.body.appendChild(iframe);

Answer 1

If I understand your situation correctly you are generating a file on the server side when you receive a request, saving it to disk and then serving it up from there. If that is what you are doing you have two options:

1. Update some shared state (memcached, redis, mongodb, a sqlite database or a file) from your generating code when you start generating the file with the total number of rows you have to generate and the number of rows you have currently generated. Make additional ajax requests back to an endpoint that will give you the current values from that shared state.
2. Stream the generated CSV file straight back to the client - unless the fetching of the data takes the majority of the time this will result in a faster appearance of the download dialog and an apparent speed up.