How to stop a iteration process in javascript?

<script src = "https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script>
  
  function Subscribe() {
    $.ajax({
      url:'https://api.thingspeak.com/update?api_key=***&field8=0',
      type:'GET',
      data:{
      type:'text'
      },
      success:function(response){
        alert(response);
          $('#singlebutton').append(data);
         }
    
    });
    setTimeout("Subscribe()", 100);
  
    }
  // second button to unsubscribe.
  function UnSubscribe() {
    $.ajax({
      url:'https://api.thingspeak.com/update?api_key=***&field8=1',
      type:'GET',
      data:{
      type:'text'
      },
      success:function(response){
        alert(response);
          $('#singlebtn').append(data);
         }
    
      });
    //setTimeout("UnSubscribe()", 100);
  }
    

</script>