var simple = [
        {
          "x": "Pepperoni",
          "y": 12
        },
        {
          "x": "Cheese",
          "y": 8
        }
      ];
var random = [];
var yMax = -1;
for(var i=0; i<8; i++) {
  var y = parseInt(Math.random()*100);
  yMax = (y>yMax) ? y : yMax;
  random.push({
    "x":"test "+i,
    "y":y
  });
};

var myData = {
  "xScale": "ordinal",
  "yScale": "linear",
  "type": "bar",
  "main": [
    {
      "className": ".pizza",
      "data": simple
    }
  ],
  "comp": [
    {
      "className": ".pizza",
      "type": "line-dotted",
      "data": [
        {
          "x": "Pepperoni",
          "y": 10
        },
        {
          "x": "Cheese",
          "y": 4
        }
      ]
    }
  ]
};

var myChart = new xChart('bar', myData, '#myChart');
var adv = myData;
adv.yMax = yMax+10;
adv.main[0].data = random;
adv.comp[0].data = random;
var myChart2 = new xChart('bar2', adv, '#myChart2');