Poltergeist - A PhantomJS driver for Capybara

Build Status

Poltergeist is a driver for Capybara. It allows you to run your Capybara tests on a headless WebKit browser, provided by PhantomJS.

If you're viewing this at https://github.com/jonleighton/poltergeist, you're reading the documentation for the master branch. View documentation for the latest release (1.1.1).


Add poltergeist to your Gemfile, and in your test setup add:

require 'capybara/poltergeist'
Capybara.javascript_driver = :poltergeist

If you were previously using the :rack_test driver, be aware that your app will now run in a separate thread and this can have consequences for transactional tests. See the Capybara README for more detail.

Installing PhantomJS

You need at least PhantomJS 1.8.1. There are no other external dependencies (you don't need Qt, or a running X server, etc.)


  • Homebrew: brew install phantomjs
  • MacPorts: sudo port install phantomjs
  • Manual install: Download this


  • Download the 32 bit or 64 bit binary.
  • Extract the tarball and copy bin/phantomjs into your PATH

Manual compilation

Do this as a last resort if the binaries don't work for you. It will take quite a long time as it has to build WebKit.

(See also the PhantomJS building guide.)


Poltergeist runs on MRI 1.9, JRuby 1.9 and Rubinius 1.9.

Ruby 1.8 is no longer supported. The last release to support Ruby 1.8 was 1.0.2, so you should use that if you still need Ruby 1.8 support.

Poltergeist does not currently support the Windows operating system.

Running on a CI

There are no special steps to take. You don't need Xvfb or any running X server at all.

Travis CI has PhantomJS pre-installed, but it might not be the latest version. If you need to install the latest version, check out the .travis.yml that Poltergeist uses.

Depending on your tests, one thing that you may need is some fonts. If you're getting errors on a CI that don't occur during development then try taking some screenshots - it may well be missing fonts throwing things off kilter. Your distro will have various font packages available to install.

What's supported?

Poltergeist supports all the mandatory features for a Capybara driver, and the following optional features:

  • page.evaluate_script and page.execute_script
  • page.within_frame
  • page.within_window
  • page.status_code
  • page.response_headers
  • cookie handling
  • drag-and-drop

There are some additional features:

Taking screenshots

You can grab screenshots of the page at any point by calling page.driver.render('/path/to/file.png') (this works the same way as the PhantomJS render feature, so you can specify other extensions like .pdf, .gif, etc.)

By default, only the viewport will be rendered (the part of the page that is in view). To render the entire page, use page.driver.render('/path/to/file.png', :full => true).

Resizing the window

Sometimes the window size is important to how things are rendered. Poltergeist sets the window size to 1024x768 by default, but you can set this yourself with page.driver.resize(width, height).

Clicking precise coordinates

Sometimes its desirable to click a very specific area of the screen. You can accomplish this with page.driver.click(x, y), where x and y are the screen coordinates.

Remote debugging (experimental)

If you use the :inspector => true option (see below), remote debugging will be enabled.

When this option is enabled, you can insert page.driver.debug into your tests to pause the test and launch a browser which gives you the WebKit inspector to view your test run with.

Read more here

Setting request headers

Additional HTTP request headers can be set like so:

page.driver.headers = { "User-Agent" => "Poltergeist" }

The extra headers will apply to all subsequent HTTP requests (including requests for assets, AJAX, etc). They will be automatically cleared at the end of the test.

Inspecting network traffic

You can inspect the network traffic (i.e. what resources have been loaded) on the current page by calling page.driver.network_traffic. This returns an array of request objects. A request object has a response_parts method containing data about the response chunks.

Manipulating cookies

The following methods are used to inspect and manipulate cookies:

  • page.driver.cookies - a hash of cookies accessible to the current page. The keys are cookie names. The values are Cookie objects, with the following methods: name, value, domain, path, secure?, httponly?, expires.
  • page.driver.set_cookie(name, value, options = {}) - set a cookie. The options hash can take the following keys: :domain, :path, :secure, :httponly, :expires. :expires should be a Time object.
  • page.driver.remove_cookie(name) - remove a cookie


You can customize the way that Capybara sets up Poltegeist via the following code in your test setup:

Capybara.register_driver :poltergeist do |app|
  Capybara::Poltergeist::Driver.new(app, options)

options is a hash of options. The following options are supported:

  • :phantomjs (String) - A custom path to the phantomjs executable
  • :debug (Boolean) - When true, debug output is logged to STDERR. Some debug info from the PhantomJS portion of Poltergeist is also output, but this goes to STDOUT due to technical limitations.
  • :logger (Object responding to puts) - When present, debug output is written to this object
  • :phantomjs_logger (IO object) - Where the STDOUT from PhantomJS is written to. This is where you console.log statements will show up. Default: STDOUT
  • :timeout (Numeric) - The number of seconds we'll wait for a response when communicating with PhantomJS. Default is 30.
  • :inspector (Boolean, String) - See 'Remote Debugging', above.
  • :js_errors (Boolean) - When false, Javascript errors do not get re-raised in Ruby.
  • :window_size (Array) - The dimensions of the browser window in which to test, expressed as a 2-element array, e.g. [1024, 768]. Default: [1024, 768]
  • :phantomjs_options (Array) - Additional command line options to be passed to PhantomJS, e.g. ['--load-images=no', '--ignore-ssl-errors=yes']
  • :extensions (Array) - An array of JS files to be preloaded into the phantomjs browser. Useful for faking unsupported APIs.
  • :port (Fixnum) - The port which should be used to communicate with the PhantomJS process. Default: 44678.


Unfortunately, the nature of full-stack testing is that things can and do go wrong from time to time. This section aims to highlight a number of common problems and provide ideas about how you can work around them.

DeadClient errors

Sometimes PhantomJS crashes during a test. There are basically two kinds of crashes: those that can be reproduced every time, and those that occur sporadically and are not easily reproduced.

If your crash happens every time, you should read the PhantomJS crash reporting guide and file a bug against PhantomJS. Feel free to also file a bug against Poltergeist in case there are workarounds that can be implemented within Poltergeist. Also, if lots of Poltergeist users are experiencing the same crash then fixing it will move up the priority list.

If your crash is sporadic, there is less that can be done. Often these issues are very complicated and difficult to track down. It may be that the crash has already been fixed in a newer version of WebKit that will eventually find its way into PhantomJS. It's still worth reporting your bug against PhantomJS, but it's probably not worth filing a bug against Poltergeist as there's not much we can do.

If you experience sporadic crashes a lot, it may be worth configuring your CI to automatically re-run failing tests before reporting a failed build.

ClickFailed errors

When Poltergeist clicks on an element, rather than generating a DOM click event, it actually generates a "proper" click. This is much closer to what happens when a real user clicks on the page - but it means that Poltergeist must scroll the page to where the element is, and work out the correct co-ordinates to click. If the element is covered up by another element, the click will fail (this is a good thing - because your user won't be able to click a covered up element either).

Sometimes there can be issues with this behavior. If you have problems, it's worth taking screenshots of the page and trying to work out what's going on. If your click is failing, but you're not getting a ClickFailed error, then you can turn on the :debug option and look in the output to see what co-ordinates Poltergeist is using for the click. You can then cross-reference this with a screenshot to see if something is obviously wrong.

If you can't figure out what's going on and just want to work around the problem so you can get on with life, consider using a DOM click event. For example, if this code is failing:

click_button "Save"

Then try:


Timing problems

Sometimes tests pass and fail sporadically. This is often because there is some problem synchronising events properly. It's often straightforward to verify this by adding sleep statements into your test to allow sufficient time for the page to settle.

If you have these types of problems, read through the Capybara documentation on asynchronous Javascript which explains the tools that Capybara provides for dealing with this.

General troubleshooting hints

  • Configure Poltergeist with :debug turned on so you can see its communication with PhantomJS.
  • Take screenshots to figure out what the state of your page is when the problem occurs.
  • Use the remote web inspector in case it provides any useful insight
  • Consider downloading the Poltergeist source and using console.log debugging to figure out what's going on inside PhantomJS. (This will require an understanding of the Poltergeist source code and PhantomJS, so it's only for the committed!)

Filing a bug

If you can provide specific steps to reproduce your problem, or have specific information that might help other help you track down the problem, then please file a bug on Github.

Include as much information as possible. For example:

  • Specific steps to reproduce where possible (failing tests are even better)
  • The output obtained from running Poltergeist with :debug turned on
  • Screenshots
  • Stack traces if there are any Ruby on Javascript exceptions generated
  • The Poltergeist and PhantomJS version numbers used
  • The operating system name and version used




  • Changed Capybara dependency to ~> 2.0.1 because Poltergeist 1.1 is not compatible with Capybara 2.1.



  • Add support for custom phantomjs loggers via :phantomjs_logger option. (Gabe Bell)
  • Add page.driver.click(x, y) to click precise coordinates. (Micah Geisel)
  • Add Capybara 2.0 support. Capybara 1.1 and Ruby 1.8 are no longer supported. (Mauro Asprea) [Issue #163]
  • Add node.base.double_click to double click the node. (Andy Shen)
  • The :debug option now causes the PhantomJS portion of Poltergeist to output some additional debug info, which may be useful in figuring out timeout errors.

Bug fixes

  • Fix timing issue when using within_frame that could cause errors. Issue #183, #211
  • Fix bug with within_frame not properly switching the context back after the block has executed. [Issue #242]
  • Fix calculation of click position when clicking within a frame. [Issue #222, #225]
  • Fix error raising when calling expires if not set on cookie. Issue #203
  • Fix the :js_errors option. Previously errors were not being reported, but would still cause commands to fail. [Issue #229]
  • Fix incorrect time zone handling when setting cookie expiry time [Issue #228]
  • Send SIGKILL to PhantomJS if it doesn't exit within 2 seconds [Issue #196]
  • Provide a more informative message for the ObsoleteNode error. [Issue #192]
  • Fix ObsoleteNode error when using attach_file with the jQuery File Upload plugin. [Issue #115]
  • Add the ability to extend the phantomjs environment via browser options. e.g. Capybara::Poltergeist::Driver.new( app, :extensions => ['file.js', 'another.js']) (@JonRowe)
  • Ensure that a String is passed over-the-wire to PhantomJS for file input paths, allowing attach_file to be called with arbitry objects such as a Pathname. (@mjtko) [Issue #215]
  • Cookies can now be set before the first request. [Issue #193]


Bug fixes

  • Clearing the value before setting a new value by sending a backspace. This fixes the issue that you can't set an empty value. [Issue #184]


Bug fixes

  • Don't use a fixed port number by default; find an available port. The port can still be configured to a fixed value using the :port option. The reverts the default behaviour to how it was before the 1.0 release. [Issue #174]



  • Click co-ordinates are shown in the debug log. You can use this in combination with page.driver.render to work out where clicks are actually happening if you are having trouble.
  • Added :port configuration option and made the default port 44678 rather than a random available port.
  • Support for Capybara's page.response_headers API to retrieve the headers of the last page load.
  • Support for cookie manipulation. [Issue #12]
  • Frame switching support now uses native PhantomJS APIs. (This might make it work better, but in general it's a badly tested area both in Capybara and Poltergeist.)
  • Support for the Capybara window switching API (page.within_window).

Bug fixes

  • Prevent TypeError: 'undefined' is not an object (evaluating 'rect.top') error when clicking an element with display: none. The click will fail, but an obsolete node error will be raised, meaning that Capybara's retry mechanisms will kick in. [Issue #130]
  • Mouse over the element we will click, before clicking it. This enables :hover effects etc to trigger before the click happens, which can affect the click in some cases. [Issue #120]
  • Don't blow up when evaluate_script is called with a cyclic structure.
  • Fix the text method for title elements, so it doesn't return an empty string.
  • Fixed problem with cookies not being clearer between tests on PhantomJS 1.7
  • Fixed Javascript errors during page load causes TimeoutErrors. [Issue #124]
  • Ensure the User-Agent header can be set successfully. (Klaus Hartl) [Issue #127]
  • Use el.innerText for Node#text. This ensures that e.g. <br> is returned as a space. It also simplifies the method. [Issue #139]
  • Fix status code support when a response redirects to another URL. This was previously tested to ensure it would return the status code of the redirected URL, but the test was falsely broken and the implementation was also broken.
  • Fixed visiting URLs where only a hash change occurs (no HTTP request). [Issue #79]
  • Setting page.driver.headers now applies the headers to all requests, not just calls to visit. (So XHR, asset requests, etc will all receive the headers.) [Issue #149]



  • Added an option :js_errors, allowing poltergeist to continue running after JS errors. (John Griffin & Tom Stuart) [Issue #62] [Issue #69]
  • Added an option :window_size, allowing users to specify dimensions to which the browser window will be resized. (Tom Stuart) [Issue #53]
  • Capybara 1.0 is no longer supported. Capybara ~> 1.1 is required.
  • Added ability to set arbitrary http request headers
  • Inspect network traffic on the page via page.driver.network_traffic (Doug McInnes) [Issue #77]
  • Added an option :phantomjs_options, allowing users to specify additional command-line options passed to phantomjs executable. (wynst) [Issue #97]
  • Scroll element into viewport if needed on click (Gabriel Sobrinho) [Issue #83]
  • Added status code support. (Dmitriy Nesteryuk and Jon Leighton) [Issue #37]

Bug fixes

  • Fix issue with ClickFailed exception happening with a negative co-ordinate (which should be impossible). (Jon Leighton, Gabriel Sobrinho, Tom Stuart) [Issue #60]
  • Fix issue with undefined method map for "[]":String, which happened when dealing with pages that include JS rewriting Array.prototype.toJSON. (Tom Stuart) [Issue #63]



  • Updated to PhantomJS 1.5.0, giving us proper support for reporting Javascript exception backtraces.



  • Detect if clicking an element will fail. If the click will actually hit another element (because that element is in front of the one we want to click), the user will now see an exception explaining what happened and which element would actually be targeted by the click. This should aid debugging. [Issue #25]
  • Click elements at their middle position rather than the top-left. This is presumed to be more likely to succeed because the top-left may be obscured by overlapping elements, negative margins, etc. [Issue #26]
  • Add experimental support for using the remote WebKit web inspector. This will only work with PhantomJS 1.5, which is not yet released, so it won't be officially supported by Poltergeist until 1.5 is released. [Issue #31]
  • Add page.driver.quit method. If you spawn additional Capybara sessions, you might want to use this to reap the child phantomjs process. [Issue #24]
  • Errors produced by Javascript on the page will now generate an exception within Ruby. [Issue #27]
  • JRuby support. [Issue #20]

Bug fixes

  • Fix bug where we could end up interacting with an obsolete element. [Issue #30]
  • Raise an suitable error if PhantomJS returns a non-zero exit status. Previously a version error would be raised, indicating that the PhantomJS version was too old when in fact it did not start at all. [Issue #23]
  • Ensure the :timeout option is actually used. [Issue #36]
  • Nodes need to know which page they are associated with. Before this, if Javascript caused a new page to load, existing node references would be wrong, but wouldn't raise an ObsoleteNode error. [Issue #39]
  • In some circumstances, we could end up missing an inline element when attempting to click it. This is due to the use of getBoundingClientRect(). We're now using getClientRects() to address this.


  • Element click position is now calculated using the native getBoundingClientRect() method, which will be faster and less buggy.
  • Handle window.confirm(). Always returns true, which is the same as capybara-webkit. [Issue #10]
  • Handle window.prompt(). Returns the default value, if present, or null.
  • Fix bug with page Javascript page loading causing problems. [Issue #19]


  • There was a bad bug to do with clicking elements in a page where the page is smaller than the window. The incorrect position would be calculated, and so the click would happen in the wrong place. This is fixed. [Issue #8]
  • Poltergeist didn't work in conjunction with the Thin web server, because that server uses Event Machine, and Poltergeist was assuming that it was the only thing in the process using EventMachine.

    To solve this, EventMachine usage has been completely removed, which has the welcome side-effect of being more efficient because we no longer have the overhead of running a mostly-idle event loop.

    [Issue #6]

  • Added the :timeout option to configure the timeout when talking to PhantomJS.


  • First version considered 'ready', hopefully fewer problems.


  • First version, various problems.


Copyright (c) 2011 Jonathan Leighton

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.