What is the process for saving a JSON object as a file?

I am currently working on allowing users to download a JSON object directly as a JSON file on my website. When using the following code, I encountered an error message:

Error: Can't set headers after they are sent.
    at SendStream.headersAlreadySent (\node_modules\send\index.js:390:13)
    at SendStream.send (\node_modules\send\index.js:617:10)
    at onstat (\node_modules\send\index.js:729:10)
    at FSReqCallback.oncomplete (fs.js:168:5)

router.post('/about', ensureAuthenticated,
  function (req, res, next) {   
    console.log(req.user);

    var jsonVariable = JSON.stringify(req.user);
    var path_tmp = create_tmp_file(jsonVariable);
    
    res.download(path_tmp);
    
    res.redirect('/about');
    next();
  }
);

Is there a more efficient way to allow for downloading a JSON object without needing to save it in the filesystem first?

javascriptexpress

Answer №1

If you want to add some custom HTML content to a page or redirect users to a new page with client-side JavaScript, there is a simple way to do it. You can pass the JSON string to the new page either through a GET parameter or any other method that suits your needs. Once on the new page, use the following code snippet to download the JSON data:

var link = document.createElement("a");
link.href = URL.createObjectURL(
    new Blob([json], {type:"application/json"})
);
link.download = "myFile.json";
link.click();

Answer №2

let jsonData = JSON.stringify(req.user);
let tempFilePath = createTemporaryFile(jsonData);
res.download(tempFilePath);

To send the data, use res.json and implement content-disposition for downloading.

res.set('Content-Disposition', 'attachment; filename=example.json')
res.json(req.user);

res.redirect('/about');
next();

Avoid this action (the cause of the error). Sending a download while redirecting to another URL is contradictory. You can't simultaneously say "Here is the file you requested" and "The requested file isn't available, go to this URL instead".

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