How to divert a number of downloads into a zip file?

I'm using the PptxGenJS library, and one of the functions I'm using it for leads to around 8 powerpoint files being downloaded at once. It works, but it creates a mess, and so putting them into a single zip file would greatly improve the experience.

The issue is that I can't find a way to do this, as there seems to be nothing in PptxGenJS that will let you manipulate a file once it's been created, it just sends it straight as a download.

Is there someway to intercept those downloads, add them to a zip file, and then send that zip to the user?

Pass in 'jszip' as the first argument of save, a callback, and a jszip file type, like this:

var p1 = new PptxGenJS();
p1.addNewSlide().addText('Presentation 1');
var p1file = p1.save('jszip', function(file1) {
    var p2 = new PptxGenJS();
    p2.addNewSlide().addText('Presentation 2');
    p2.save('jszip', function(file2) {
        var zip = new JSZip();
        zip.file('pres1.pptx', file1);
        zip.file('pres2.pptx', file2);

        zip.generateAsync({type: 'blob'}).then(function(content) {
            saveAs(content, 'multipres.zip'); // requires filesaver.js
        });
    }, 'blob');
}, 'blob');

If you have more than 2 presentations to file, you'll probably want to use async instead of nested callbacks.