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POHow to download, zip and save multiple files with Javascript and get progress?
 

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  1. POHow to download, zip and save multiple files with Javascript and get progress?
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    <p>I'm creating a Chrome extension that needs to download multiple files (images and/or videos) from a website. These files may have a huge size, so I want to show the download progress to the user. After some research I found that currently a possible solution might be: </p> <ol> <li>Download all the files with XMLHttpRequests.</li> <li>When downloaded, zip all the files into one archive with a JavaScript library (eg. JSZip.js, zip.js).</li> <li>Prompt the user to save the zip with SaveAs dialog.</li> </ol> <p>I'm stuck at passage 2), how can I zip the downloaded files?</p> <p>To understand, here is a code sample:</p> <pre><code>var fileURLs = ['http://www.test.com/img.jpg',...]; var zip = new JSZip(); var count = 0; for (var i = 0; i &lt; fileURLs.length; i++){ var xhr = new XMLHttpRequest(); xhr.onprogress = calculateAndUpdateProgress; xhr.open('GET', fileURLs[i], true); xhr.responseType = "blob"; xhr.onreadystatechange = function () { if (xhr.readyState == 4) { var blob_url = URL.createObjectURL(response); // add downloaded file to zip: var fileName = fileURLs[count].substring(fileURLs[count].lastIndexOf('/')+1); zip.file(fileName, blob_url); // &lt;- here's one problem count++; if (count == fileURLs.length){ // all download are completed, create the zip var content = zip.generate(); // then trigger the download link: var zipName = 'download.zip'; var a = document.createElement('a'); a.href = "data:application/zip;base64," + content; a.download = zipName; a.click(); } } }; xhr.send(); } function calculateAndUpdateProgress(evt) { if (evt.lengthComputable) { // get download progress by performing some average // calculations with evt.loaded, evt.total and the number // of file to download / already downloaded ... // then update the GUI elements (eg. page-action icon and popup if showed) ... } } </code></pre> <p>The upper code generate a downloadable archive containing small corrupted files. There is also an issue with filename sync: blob object do not contains the file name, so If eg. <code>fileURLs[0]</code> takes more time to be downloaded than <code>fileURLs[1]</code> names become wrong (inverted).. </p> <p>NOTE: I know that Chrome has a download API but it's in dev channel so unfortunately it's not a solution now, and I would like to avoid using NPAPI for such a simple task.</p>
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    1. USSimon Adcock
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    1. COAs I read the question, you want to zip all images and provide one zip as a download, right? Then the answer from that other question is 100% applicable. Substitute the URL for a data-URL or blob-URL which you generate using the zip library of your choice. If you want an example, feel free to look in the source code of my [Chrome extension source viewer](https://chrome.google.com/webstore/detail/chrome-extension-source-v/jifpbeccnghkjeaalbbjmodiffmgedin) extension. `popup.js` shows the code to initiate a download of a generated zip file.
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      1. USRob W
    2. COI see that you've attempted to copy the code from my extension without understanding it, is that correct? If so, read the documentation for zip.js and get back when you're stuck or if something is unclear: http://gildas-lormeau.github.io/zip.js/core-api.html
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      1. POHow to download, zip and save multiple files with Javascript and get progress?
      1. USRob W
    3. COfrom your extension (useful) I used just the code to trigger the download, the problem is not there, it's with passing downloaded file binary data to the zip library, I don't understand how it has to be done since I haven't found any related documentation.
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