How can I retrieve user input in window prompt in python flask?

Question

So I know how to use forms to fetch user input in python flask, however, I want to allow the user to input text in a window popup prompt (I can activate this in javascript), then send this data straight to flask on submission. The problem is that I don't know how to give flask this information since it is in the scope of javascript. May I please know how I can do this?

Thanks in advance!

Edit: MWE code (I hope this has enough detail.)

<!-- students.html -->
<form method="POST", action="/students">
    <button name="remove_student_button" value={{ student.email }} onClick="myFunction()">Remove</button>
</form>

<script>

    function myFunction() {
        let person = prompt("Are you sure you want to remove this entry? Enter the student's email to confirm your action.");
        if (person == null || person == "") {
            // Cancelled. Nothing happens
        } else {
            // Run form method which activates /students.
        }
    }

</script>

# routes.py
@app.route("/students", methods = ["GET", "POST"])
def students():
    # ...
    if "remove_student_button" in request.form:
        email = request.form["remove_student_button"]
        student = Student.query.filter_by(email=email).first()
        print(student.first_name)
        db.session.commit()
        flash("Student removed")
        return redirect(url_for("students", student_removed=True))
    # ...