Как выбрать option в select

window.onload = function() { 
  var eSelect = document.getElementById('select'); 
  eSelect.onchange = function() { 
    var nOm = eSelect.options[this.selectedIndex].getAttribute('data-id'); 
    console.log(nOm); 
  } 
}

<div id="sel"> 
  <select id="select" data-ids="1"> 
    <option class="test1" data-id="1">Selection 1</option> 
    <option class="test2" data-id="2">Selection 2</option> 
    <option class="test3" data-id="3">Selection 3</option> 
  </select> 
</div>