PacMan's new Ghost Bindy.

CasperJS and PhantomJS are fantastic tools for creating integration tests to sanity check the complete functionality of your site. They can simulate a user, click and keydown through your UI and take screenshots of your page. Written in javascript, tests are lean and do not require the heft of the alternative browser driver Selenium.

Recently I ran into an issue with CasperJS while taking screenshots. I received TypeError: 'undefined' is not a function (evaluating 'a.createDescriptor.bind(null,t)'). I was using the most recent stable versions of CasperJS 1.1.0-beta3 and PhantomJS 1.9.7.

It turns out that PhantomJS below version 2.0.0 does not include the .bind() function. It is recommended to download the latest 2.0 version of PhantomJS from the master branch and use CasperJS with that build. After working through unrelated issues with PhantomJS 1.9.8 and downgrading to 1.9.7 I was not interested in trying out an even more unstable version.

For me, the answer was to patch in the bind function to the evaluated remote page as shown below.

 * CasperJS .bind()
 * Adds .bind() capability missing from PhantomJS < 2.0.0 for CasperJS.
 * Needed for some types of evaluations on the remote page as well as
 * screenshots.
casper.on('page.initialized', function() {
  casper.evaluate(function() {
    var isFunction = function(o) {
      return typeof o == 'function';

    var bind;
    var slice = [].slice;
    var proto = Function.prototype;
    var featureMap;

    featureMap = {
      'function-bind': 'bind'

    function has(feature) {
      var prop = featureMap[feature];
      return isFunction(proto[prop]);

    if (!has('function-bind')) {
      bind = function bind(obj) {
        var args =, 1);
        var self = this;
        var nop = function() {};
        var bound = function() {
          return self.apply(this instanceof nop ? this : (obj || {}), args.concat(;
        nop.prototype = this.prototype || {};
        bound.prototype = new nop();
        return bound;
      proto.bind = bind;

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CasperJS, PhantomJS, Javascript