const zip = new JSZip();
zip.file("Hello.txt", "Hello World\n");
const img = zip.folder("images");
img.file("smile.gif", imgData, {base64: true});
zip.generateAsync({type:"blob"}).then(function(content) {
    // see FileSaver.js
    saveAs(content, "example.zip");
});
/*
Results in a zip containing
Hello.txt
images/
    smile.gif
*/