Here's a selection of the most frequently asked questions by casperjs newcomers.

Is CasperJS a nodejs library?

No. CasperJS is written on top of PhantomJS, which is a node-independent Qt/Webkit based library. If you try to run your CasperJS script with node or coffee, it just won't work

Hint If you want to use CasperJS with node, try SpookyJS.

I'm stuck! I think there's a bug! What can I do?

Before rage-tweeting:

3. Check you're running the latest stable tag
5. Ask on the project mailing list:
• try to post a reproducible, minimal test case
• compare casperjs results with native phantomjs ones
• if the problem also occurs with native phantomjs, ask on phantomjs mailing list
6. Eventually, file an issue.

I keep copy and pasting stuff in my test scripts, that's boring

Have a look at this gist, it might help.

Also, don't forget that CasperJS supports a CommonJS-compliant module pattern implementation. Note that CasperJS' implementation differs a bit from the one provided by PhantomJS, but I personnaly never really encountered any functional difference.

What is the versioning policy of CasperJS?

Releases will follow the SemVer standard; they will be numbered with the follow format:

<major>.<minor>.<patch>[-<identifier>]

And constructed with the following guidelines:

• Breaking backwards compatibility bumps the major
• New additions without breaking backwards compatibility bumps the minor
• Bug fixes and misc changes bump the patch
• Unstable, special and trunk versions will have a proper identifier

Can I use jQuery with CasperJS?

Sure, as every single other javascript library on Earth.

A first solution is to inject it into the remote DOM environment by hand using the standard WebPage.injectJs() method:

casper.page.injectJs('/path/to/jquery.js');

If you need jQuery being available everytime, you can also make it being injected in every received response by setting the clientScripts option of CasperJS:

var casper = require('casper').create({
clientScripts: ["includes/jquery.min.js"]
});

Note You can't inject scripts using the HTTP protocol, you actually have to use a relative/absolute filesystem path to the script resource.

Can I use CasperJS without using the casperjs executable?

Yes, you can call a CasperJS script directly with the phantomjs executable, but if you do so, you must set the phantom.casperPath property to the path where the library root is located on your system:

// casperscript.js
phantom.casperPath = '/path/to/casperjs';
phantom.injectJs(phantom.casperPath + '/bin/bootstrap.js');

var casper = require('casper').create();
// ...

You can run such a script like any other standard PhantomJS script:

$phantomjs casperscript.js If you're on Windows, this is the way you may manage to get casper working the most easily: phantom.casperPath = 'C:\\path\\to\\your\\repo\\lib\\casperjs-0.6.X'; phantom.injectJs(phantom.casperPath + '\\bin\\bootstrap.js'); var casper = require('casper').create(); // do stuff How can I catch HTTP 404 and other status codes? You can define your own HTTP status code handlers by using the httpStatusHandlers option of the Casper object. You can also catch other HTTP status codes as well, as demoed below: var casper = require('casper').create(); casper.on('http.status.404', function(resource) { this.echo('wait, this url is 404: ' + resource.url); }); casper.on('http.status.500', function(resource) { this.echo('woops, 500 error: ' + resource.url); }); casper.start('http://mywebsite/404', function() { this.echo('We suppose this url return an HTTP 404'); }); casper.thenOpen('http://mywebsite/500', function() { this.echo('We suppose this url return an HTTP 500'); }); casper.run(function() { this.echo('Done.').exit(); }); Hint Check out all the other cool events you may use as well. What's this mysterious __utils__ object? The __utils__ object is actually an instance of the ClientUtils class which have been automatically injected into the page DOM and is therefore always available. So everytime to perform an evaluate() call, you have this instance available to perform common operations like: • fetching nodes using CSS3 or XPath selectors, • retrieving information about element properties (attributes, size, bounds, etc.), • sending AJAX requests, • triggering DOM events Check out the whole API. You even have a bookmarklet to play around with this __utils__ instance right within your browser console! Note You're not obliged at all to use the __utils__ instance in your scripts. It's just there because it's used by CasperJS internals. How does then() and the step stack work? Disclaimer This entry is based on an answer I made on Stack Overflow. The then() method basically adds a new navigation step in a stack. A step is a javascript function which can do two different things: 1. waiting for the previous step - if any - being executed 2. waiting for a requested url and related page to load Let's take a simple navigation scenario: var casper = require('casper').create(); casper.start(); casper.then(function step1() { this.echo('this is step one'); }); casper.then(function step2() { this.echo('this is step two'); }); casper.thenOpen('http://google.com/', function step3() { this.echo('this is step 3 (google.com is loaded)'); }); You can print out all the created steps within the stack like this: require('utils').dump(casper.steps.map(function(step) { return step.toString(); })); That gives: $ casperjs test-steps.js
[
"function step1() { this.echo('this is step one'); }",
"function step2() { this.echo('this is step two'); }",
"function _step() { this.open(location, settings); }",
]

Notice the _step() function which has been added automatically by CasperJS to load the url for us; when the url is loaded, the next step available in the stack — which is step3() — is then called.

When you have defined your navigation steps, run() executes them one by one sequentially:

casper.run();

Note The callback/listener stuff is an implementation of the Promise pattern.

Is it possible to achieve parallel browsing using CasperJS?

Officially no, but you may want to try.

Okay, honestly, I'm stuck with Javascript.

Don't worry, you're not alone. Javascript is a great language, but it's far more difficult to master than one might expect at first look.

Here are some great resources to get started efficiently with the language:

FAQ list

Contribute If you want to contribute FAQs to this section, feel free to fork the documentation pages branch on github, and send me a pull request with your tips and tricks!