How to send data from js file to another js file through flask?

I am making a simple app where I have to send certain data from one html file to another through flask.

home.html

<a href="ocr">
    <button type="submit" class="btn" id="submit">GO!!</button>
</a>

home.js

btn.addEventListener('click', function (e) {
            fetch('/ocr', {
                headers: {
                    'Content-Type': 'application/json',
                },
                method: 'POST',
                body: JSON.stringify(s),
            });
        });

server.py

@app.route("/", methods=["GET", "POST"])
def root():
    return render_template("home.html")


@app.route("/ocr", methods=["GET", "POST"])
def ocr():
    output = request.get_json()
    result = json.loads(output)
    #I want to take the result from here to index.html as json
    #return render_template("index.html")

If I uncomment the render_template line, flask is throwing the following error.

Bad Request
Did not attempt to load JSON data because the request Content-Type was not 'application/json'.

How do I solve this?

source https://stackoverflow.com/questions/72636890/how-to-send-data-from-js-file-to-another-js-file-through-flask