<input class="pg-page-num" type="text" name="" value="34/233" id="pageNum">
<input type="hidden" name="" value="25" id="totalPage">

<script type="text/javascript">
  var oPage = document.querySelector('#pageNum'),
    oTotal = document.querySelector('#totalPage'),
    sOldVal = '';

  oPage.addEventListener('focus', function () {
    this.type = 'number';
    sOldVal = this.value;
  }, false);

  oPage.addEventListener('blur', function () {
    var sVal = this.value;
    this.type = 'text';
    if (sVal != sOldVal) {
      this.value += '/' + oTotal.value;
    }
  }, false);
</script>