Attempt at monkeypatching casper

gistfile1.js

casper.fetchTextArray = function fetchTextArray(selector) {
  console.log(this);
  var text = '';
  var elements = this.findAll(selector);
  if (elements && elements.length) {
    Array.prototype.forEach.call(elements, function _forEach(element) {
    	if(text === '')
        text = element.textContent || element.innerText;
      else
      	text = [text].push(element.textContent || element.innerText);
    });
  }
  return text;
};

TypeError: 'undefined' is not a function (evaluating 'this.findAll(selector)') in fetchTextArray