[Vlasenko Fedor]

<input type="text" data-action="13" id="qsymbols" />
<script>
  var inp = document.getElementById("qsymbols");
  var action = inp.getAttribute("data-action");
  inp.oninput= function () {
    this.value = this.value.replace(/\D/g, '');
    if (action == this.value.length) {
      alert("Worked. Value length = " + action);
    }
  }
</script>