Edit in JSFiddle

var DataProvider = function () {}


DataProvider.prototype.getHeader() = function () {
  return ['col1', 'col2', 'col3', 'col4'];
}

DataProvider.prototype.getData() = function () {
  return [
    ['val1', 'val2', 'val3', 'val4'], 
    ['val5', 'val6', 'val7', 'val8']
  ];
}