Fabric.js subclass working example, supporting clone - LabeledRect

example.js

    fabric.LabeledRect = fabric.util.createClass(fabric.Rect, {

      type: 'labeledRect',

      toObject: function() {
        return fabric.util.object.extend(this.callSuper('toObject'), {
          label: this.get('label')
        });
      },

      _render: function(ctx) {
        this.callSuper('_render', ctx);

        ctx.font = '20px Helvetica';
        ctx.fillStyle = '#333';
        ctx.fillText(this.label, -this.width/2, -this.height/2 + 20);
      }
    });

    fabric.LabeledRect.fromObject = function(object, callback) {
      return fabric.Object._fromObject('LabeledRect', object, callback);
    };

    var labeledRect = new fabric.LabeledRect({
      width: 100,
      height: 50,
      left: 600,
      top: 100,
      label: 'test',
      fill: '#faa'
    });

    canvas.add(labeledRect);

    labeledRect.clone((cloned) => {
      cloned.set({
        left: cloned.left + 50,
        top: cloned.top + 70,
      });
      canvas.add(cloned);
    });

The official example is not very correct.

Here's the working one.