Button is redirecting on click but I want it to also pass a value

Question

I have an html table calendar with the dates set to buttons. When a user clicks on the button, the button will redirect them to the appointments page. However, I need it to pass the value of the button, set to its respective date, to the appointments page as well so the user can book a meeting on that date.

<button type="button" value = "1" onclick="window.location.href='{{ url_for( 'appointments') }}';">1</button>

I would like to pass the value "1" to /appointments page when I click the button but I do not know how to do so. Is it possible to do this? Im doing this on flask python.

Appointments.html

{% extends 'base.html' %}

    {% block body %}
    <div class="container">
        <form method="POST" action="/appointments">
            <h2>Appointments</h2>
            <p>
                {{ form.start.label }}<br>
                {{ form.start }}
            </p>

            <p>
                {{ form.end.label }}<br>
                {{ form.end }}
            </p>

            <p>
                {{ form.description.label }}<br>
                {{ form.description }}
            </p>

            <p>
                {{ form.guestName.label }}<br>
                {{ form.guestName }}
            </p>
            <input type="submit">
            <!-- <button class = "btn btn btn-primary btn block" type="submit">Set up</button> -->
        </form>

    </div> <!-- /container -->
    {% endblock %}

Appointment route:

@app.route('/appointments', methods=['GET', 'POST'])
def appointments():

    form = AddAppointment()
    if form.is_submitted():

        startingTime = datetime.datetime.strptime(
            form.start.data, '%H:%M').time()
        endingTime = datetime.datetime.strptime(form.end.data, '%H:%M').time()
        print(startingTime, endingTime)
        appt = Appointments(starttime=form.start.data, endtime=form.end.data,
                            description=form.description.data, guestName=form.guestName.data)
        print(appt)
        db.session.add(appt)
        db.session.commit()
        return redirect('/dashboard')

    return render_template('appoitments.html', form=form)

Answer 1

A quick fix is to add a hidden input field to the form, i.e. <input type="hidden" name="<field_name>" value="1" />. See this answer.

If that doesn't work, you can use javascript with an xml request, usually promise-ified with axios or fetch, to send the form data. It might be overkill for what you're trying to do, though.