title: using fabric.js ,increase fontSize of canvas text on button click
body: <p>i am using fabric.js to work on canvas . i have created text on canvas .now,onclick of  button i want to increase font-size .</p>
  
  <pre><code>canvas.set({fontSize,40});
  </code></pre>
  
  <p>this is not working ? any other method .i have created fiddle please  <a href="http://jsfiddle.net/BTh6A/4/" rel="noreferrer">Check</a></p>
  
  <pre><code>   var canvas = window._canvas = new fabric.Canvas('c');
  var text = new fabric.Text('Sample', {
      left: 100,
      top: 100,
      fill: 'navy'
  });
  
  canvas.add(text);
  
  document.getElementById('textinput').addEventListener('change', function (e) {
      var obj = canvas.getActiveObject();
  
      if (!obj) return;
  
      obj.setText(e.target.value);
      canvas.renderAll();
  });
  
  document.getElementById('btn').addEventListener('click', function (e) {
      var obj = canvas.getActiveObject();
  
     alert('button clicked');
       if (!obj) return;
  
      obj.set(fontSize,40);
      canvas.renderAll();
  });
  </code></pre>