JSFiddle - React, Tailwind, and code Playground

HTML

<form role="form" id="mc-form" method="POST" action="localhost/test.php">
    <div class="input-group">
        <input id="zahl" type="email" class="form-control" placeholder="nummer" required  name="EMAIL">
        <span class="input-group-btn">
            <button id="button" type="submit" class="btn btn-default" id="mc-subscribe" value="Subscribe" name="subscribe">
                Daten/Status abrufen
            </button>
        </span>
    </div>
</form>

JavaScript

var formLink;
    var input;
    window.onload=function(){
        button = document.getElementById('button');
        button.onclick = function(){
            zeigeVars();
            aendereLink();
            zeigeVars();
        }
        formLink = document.getElementById('mc-form').action;
        input = document.getElementById('zahl');
    }
    function zeigeVars(){
        alert(formLink+"\n---\n"+input.value);
    }
    function aendereLink(){
        formLink = formLink+"/"+input.value;
    }