How to add a preloader for a site?

Question

Joomla

The site has such functionality (implemented on flask) - a file is applauded through a form, then this file is processed for quite a long time, up to a minute. After processing is complete, a redirect to a new page with the output of the result occurs. I need some kind of js stub at the time of processing. I copied and pasted in the front at the level. I found a couple of options for ready-made scripts, but they only work at the time of the initial load of the page with the form. How to make the script run at the right time? I suppose that you need to dance from the server response 200, but I don’t know which side to take. And how to set the start time of the script is the same mystery.

@app.route("/done/<count>")
def result(count=0):
    count = count
    return render_template('result.html', count=count)

@app.route('/', methods=['GET', 'POST'])
def index():
    if request.method == 'POST':
        ........
        #Upload and save img file logic
        ......
            img = (os.path.join(app.config['UPLOAD_FOLDER'], filename))
            detection, count = performDetect(imagePath = img)#эта фунция обрабатывает файл и возвращает detection и count , в момент выполнения нужна заглушка
            #Спустя время затраченное на выполнение performDetect происходит редирект
            return redirect(url_for("result", count=count))
            
    return render_template("index.html")

Answer 1

while uploading a file, just put a gif image of a file upload like this
and the response will still be a redirect

Answer 2

Found the answer on stackoverflow https://stackoverflow.com/questions/14525029/displ...