Error event handlers for PhantomJS and CasperJS: PhantomJS and CasperJS don't show errors on the page by default. This can give clues as to what did go wrong.

1_phantomErrors.js

var page = require('webpage').create(),
    url = 'http://example.com/';

// Put the event handlers somewhere in the code before the action of 
// interest (opening the page in question or clicking something)

// http://phantomjs.org/api/webpage/handler/on-console-message.html
page.onConsoleMessage = function(msg, lineNum, sourceId) {
  console.log('CONSOLE: ' + msg + ' (from line #' + lineNum + ' in "' + sourceId + '")');
};

// http://phantomjs.org/api/webpage/handler/on-error.html
page.onError = function(msg, trace) {
  var msgStack = ['ERROR: ' + msg];
  if (trace && trace.length) {
    msgStack.push('TRACE:');
    trace.forEach(function(t) {
      msgStack.push(' -> ' + t.file + ': ' + t.line + (t.function ? ' (in function "' + t.function +'")' : ''));
    });
  }

  console.error(msgStack.join('\n'));
};

// http://phantomjs.org/api/webpage/handler/on-resource-error.html
page.onResourceError = function(resourceError) {
  console.log('Unable to load resource (#' + resourceError.id + ' URL:' + resourceError.url + ')');
  console.log('Error code: ' + resourceError.errorCode + '. Description: ' + resourceError.errorString);
};

// http://phantomjs.org/api/webpage/handler/on-resource-timeout.html
page.onResourceTimeout = function(request) {
    console.log('Response Timeout (#' + request.id + '): ' + JSON.stringify(request));
};

// use other helpful event handlers to debug the page behavior are:
//   onNavigationRequested
//   onResourceReceived
//   onResourceRequested
//   onUrlChanged

page.open(url, function(status) {
  console.log('Status: ' + status);
  phantom.exit();
});

2_casperErrors.js

var casper = require('casper').create({
    // these options only show some behavior of the page, but rarely any helpful errors
    verbose: true,
    logLevel: "debug"
});
var url = 'http://example.com/';

// http://docs.casperjs.org/en/latest/events-filters.html#remote-message
casper.on("remote.message", function(msg) {
    this.echo("Console: " + msg);
});

// http://docs.casperjs.org/en/latest/events-filters.html#page-error
casper.on("page.error", function(msg, trace) {
    this.echo("Error: " + msg);
    // maybe make it a little fancier with the code from the PhantomJS equivalent
});

// http://docs.casperjs.org/en/latest/events-filters.html#resource-error
casper.on("resource.error", function(resourceError) {
    this.echo("ResourceError: " + JSON.stringify(resourceError, undefined, 4));
});

// http://docs.casperjs.org/en/latest/events-filters.html#page-initialized
casper.on("page.initialized", function(page) {
    // CasperJS doesn't provide `onResourceTimeout`, so it must be set through 
    // the PhantomJS means. This is only possible when the page is initialized
    page.onResourceTimeout = function(request) {
        console.log('Response Timeout (#' + request.id + '): ' + JSON.stringify(request));
    };
});

casper.start(url).run();

3_phantomNodeErrors.js

var phantom = require('phantom');

phantom.create(function (ph) {
  ph.createPage(function (page) {
    // Put the event handlers somewhere in the code before the action of 
    // interest (opening the page in question or clicking something)
    // See https://github.com/sgentle/phantomjs-node#functionality-details for proper use of callbacks

    // http://phantomjs.org/api/webpage/handler/on-console-message.html
    page.set('onConsoleMessage', function(msg, lineNum, sourceId) {
      console.log('CONSOLE: ' + msg + ' (from line #' + lineNum + ' in "' + sourceId + '")');
    });

    // http://phantomjs.org/api/webpage/handler/on-error.html
    page.set('onError', function(msg, trace) {
      var msgStack = ['ERROR: ' + msg];
      if (trace && trace.length) {
        msgStack.push('TRACE:');
        trace.forEach(function(t) {
          msgStack.push(' -> ' + t.file + ': ' + t.line + (t.function ? ' (in function "' + t.function +'")' : ''));
        });
      }

      console.error(msgStack.join('\n'));
    });

    // http://phantomjs.org/api/webpage/handler/on-resource-error.html
    page.set('onResourceError', function(resourceError) {
      console.log('Unable to load resource (#' + resourceError.id + ' URL:' + resourceError.url + ')');
      console.log('Error code: ' + resourceError.errorCode + '. Description: ' + resourceError.errorString);
    });

    // http://phantomjs.org/api/webpage/handler/on-resource-timeout.html
    page.set('onResourceTimeout', function(request) {
        console.log('Response Timeout (#' + request.id + '): ' + JSON.stringify(request));
    });
    page.open("https://www.google.com", function (status) {
      console.log("opened google? ", status);
      page.evaluate(function () { return document.title; }, function (result) {
        console.log('Page title is ' + result);
        ph.exit();
      });
    });
  });
}, /* on Windows only: */ {
  dnodeOpts: {
    weak: false
  }
});

4_horsemanErrors.js

var Horseman = require('node-horseman');
var horseman = new Horseman();

horseman
  .on("consoleMessage", function(msg){
    console.log('CONSOLE: ' + msg);
  })
  .on("error", function(msg, trace){
    var msgStack = ['ERROR: ' + msg];
    if (trace && trace.length) {
      msgStack.push('TRACE:');
      trace.forEach(function(t) {
        msgStack.push(' -> ' + t.file + ': ' + t.line + (t.function ? ' (in function "' + t.function +'")' : ''));
      });
    }
    console.error(msgStack.join('\n'));
  })
  .on("resourceError", function(resourceError){
    console.log('Unable to load resource (#' + resourceError.id + ' URL:' + resourceError.url + ')');
    console.log('Error code: ' + resourceError.errorCode + '. Description: ' + resourceError.errorString);
  })
  .on("resourceTimeout", function(request){
    console.log('Response Timeout (#' + request.id + '): ' + JSON.stringify(request));
  })
  .open('http://www.google.com')
  .close();