<----- BODY ----->

  <button id="start" onclick="start_Int()">Start</button>
  <button id="ende" onclick="stop_Int()">Ende</button>
  <div style="display:flex;" id="count"></div>

<----- SCRIPT ----->

  var intval="";

    function start_Int(){
      intval=window.setInterval("start_count()",1000);
    }

    function stop_Int(){


          window.clearInterval(intval)


    }
  function start_count(){
      var p = document.createElement('p');
   p.appendChild(document.createTextNode('+'));

   document.getElementById('count').appendChild(p);
  }