Fabric js: Increase font size instead of just scaling when resize with mouse

var canvas = new fabric.Canvas('canvas');
$(document).ready(function() {
  $('#text-font-size').keyup(function() {
    var val = $(this).val();
    if (isNaN(val)) {
      alert('please enter number');
      $(this).val('');
    }
    var activeObject = canvas.getActiveObject();
    activeObject.fontSize = val;
    canvas.renderAll();
  });
  $('#add-text-btn').click(function() {
    if ($('#text-font-size').val()) {
      var txtfontsize = $('#text-font-size').val();
    } else {
      var txtfontsize = 40;
    }
    var message = $('#add-text-value').val();
    //var txtfontfamily = $('#font-family').val();
    var new_text = new fabric.IText(message, {
      left: 100,
      top: 100,
      fontSize: txtfontsize,
      lockUniScaling: true,
      //fontFamily: txtfontfamily,
      fill: '#000'
    });
    canvas.add(new_text);
    canvas.setActiveObject(new_text);
  });

  canvas.on('object:selected', function(options) {
    if (options.target) {
      $("textarea#add-text-value").val(options.target.text);
      $("#text-font-size").val(options.target.fontSize);
    }
  });

  canvas.on('object:scaling', function(event) {
    if (event.target) {
      $("textarea#add-text-value").val(event.target.text);
      $("#text-font-size").val((event.target.fontSize * event.target.scaleX).toFixed(0));
    }
  });

  canvas.on('object:modified', function(event) {
    if (event.target) {
      event.target.fontSize *= event.target.scaleX;
      event.target.fontSize = event.target.fontSize.toFixed(0);
      event.target.scaleX = 1;
      event.target.scaleY = 1;
      event.target._clearCache();
      $("textarea#add-text-value").val(event.target.text);
      $("#text-font-size").val(event.target.fontSize);
    }
  });

});

<script src="//cdnjs.cloudflare.com/ajax/libs/fabric.js/1.5.0/fabric.min.js"></script>
<script src="//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button id="add-text-btn">Add text</button>
<br>
<br>
<textarea rows="7" id="add-text-value">Your Text Here</textarea>
<br>
<input id="text-font-size" placeholder="fontsize" type="number" class="form-control">
<canvas id='canvas' width="500" height="400" style="border:#000 1px solid;"></canvas>