So I want the user to write in an email in the input field, and then I want to take that input when the button is clicked, without changing page, as it ruins my routes.
<input type="email" class="form-control" id="email" placeholder="Add Navigators Email so they can access the Session">
<button type="button" onclick="addNav()" class="btn btn-success">Add to Session</button><br>
You have to find the element by it's id and then get it's value:
email_input = document.getElementById("email"); alert(email_input.value);
Working example: https://jsfiddle.net/gbenussi/dusoctra/