join_files_and_download_in_frontend.js

import JSZip from 'jszip';
import JSZipUtils from 'jszip-utils';
import saveAs from 'file-saver';
 
function urlToPromise(url) {
    return new Promise(function(resolve, reject) {
        JSZipUtils.getBinaryContent(url, function (err, data) {
            if(err) {
                reject(err);
            } else {
                resolve(data);
            }
        });
    });
}
 
function saveFilesToZip() {
    const zip = new JSZip();
    const folder_name = 'folder_name'
    zip.folder(folder_name);
  
    const url = 'http://www.url_file.extension'
    const pdf_name = 'pdf_name.extension'
    zip.file(`${folder_name}/${pdf_name}.pdf`, urlToPromise(url), {binary:true});
  
    zip.generateAsync({type:"blob"})
    .then(function(content) {
        zip_name = 'zip_name.zip'
        saveAs(content, zip_name);
    });
}