Use AJAX to upload a file, process, and return a result to Javascript using Flask

Question

I've figured out how to upload a file using AJAX and Flask such that the page doesn't refresh and the file is uploaded to the server in some specified directory. In the Python method (upload()), I want to process the filename with some regex and return an array to the Javascript file. Do I still return render_template(index.html), even if I'm trying to request an array?

HTML (index.html)

<form id="upload-file" role="form" action="sendQuestions" method="post" enctype="multipart/form-data">
    <div class="modal-body">
        <label for="file"><b>Upload packet here</b></label>
        <input type="file" name="file">
        <p class="help-block">Upload a .pdf or .docx file you want to read.</p>
    </div>
    <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
        <button id="upload-file-btn" type="button" class="btn btn-primary" data-dismiss="modal" value="Upload">Upload</button>
    </div>
</form>

Javascript

$(function() {
    $('#upload-file-btn').click(function() {
        var form_data = new FormData($('#upload-file')[0]);
        $.ajax({
            type: 'POST',
            url: '/uploadajax',
            data: form_data,
            contentType: false,
            cache: false,
            processData: false,
            async: false,
            success: function(data) {
                console.log('Success!');
            },
        });
    });
});

Python (Flask)

@app.route('/uploadajax', methods=['POST'])
def upload():
    file = request.files['file']

    if file and allowed_file(file.filename):
         filename = secure_filename(file.filename)
         file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))

    return render_template('index.html')

I'm playing around with adding this AJAX call in the Javascript after the $.ajax{} part, but did I do it right? I'm not sure if I can call the same Python method twice in one Javascript function, or if there's an entirely better way to do this.

ajaxRequest = ajaxFunction()
    ajax.onreadystatechange = function() {
        if (ajaxRequest.readyState === 4) {
            if (ajaxRequest.status === 200) {
                alert(ajaxRequest.responseText) //I want the Python to put the array into this ajaxRequest.responseText variable, not sure how.
            }
            else
                alert('Error with the XML request.')
        }
    }
    ajaxRequest.open("GET", 'uploadajax', true);
    ajaxRequest.send(null);

Any help? Thanks.

Answer 1

You don't say what you want to achieve (hide some div, scroll window ...), and that's a main problem. To sum what should be done :
Don't return

return render_template('index.html')

but fe. if you want to notify the user about the upload status, make status for this call like

return Response('OK')

or other status - NOTOK or something. Then in the js :

    success: function(data) {
        console.log('Success!');
    },

manipulate the response

if (data == 'OK') {
  alert ('YAY, FILE UPLOADED');
};