<input type="checkbox"/>
<button>here</button>
<span></span>
<script>
  var c = document.querySelector('input');
var span = document.querySelector('span');
var button = document.querySelector('button');
c.indeterminate = true;
var f = function() {
  var elm = c;
  span.innerHTML = elm.checked + " : " + elm.indeterminate;
};
c.addEventListener('click', f);
button.addEventListener('click', f);
</script>