FAQ

Is CasperJS a node.js 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, it just won’t work out of the box.

Hint

If you want to drive CasperJS from node, try SpookyJS.

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

Before rage-tweeting:

  1. Read the docs
  2. Check if an issue has been open about your problem already
  3. Check you’re running the latest stable tag
  4. Check you’re running the latest version of PhantomJS
  5. Ask on the project mailing list:
    1. try to post a reproducible, minimal test case
    2. compare casperjs results with native phantomjs ones
    3. if the problem also occurs with native phantomjs, ask on phantomjs mailing list
  6. Eventually, file an issue.

The casper.test property is undefined, I can’t write any test!

That’s because as of 1.1, the casper.test property is only set to a Tester instance when using the casperjs test subcommand.

You may want to read the testing documentation for more information.

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

CasperJS’ implementation of require() differs a bit from the one provided by PhantomJS, but I personally never 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, you can use jQuery, 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');

In the event that you require jQuery being available on every page, you can make use of 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.

Where does CasperJS write its logfile?

Nowhere. CasperJS doesn’t write logs on the filesystem. You have to implement this by yourself if needed.

What’s this mysterious __utils__ object?

The __utils__ object is actually a ClientUtils object 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 operation 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); }",
    "function step3() { this.echo('this is step 3 (google.com is loaded)'); }"
]

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.

I’m having hard times downloading files using download()

You should try to disable web security. Using the --web-security command line option:

$ casperjs --web-security=no myscript.js

Within code:

var casper = require('casper').create({
    pageSettings: {
        webSecurityEnabled: false
    }
});

Or anytime:

casper.page.settings.webSecurityEnabled = false;

Can I access & manipulate DOM elements directly from the CasperJS environment?

No. Like in PhantomJS, you have to use Casper#evaluate() to access actual page DOM and manipulate elements.

For example, you can’t do this:

// this won't work
casper.then(function() {
    var titleNode = document.querySelector('h1');
    this.echo('Title is: ' + titleNode.textContent);
    titleNode.textContent = 'New title';
    this.echo('Title is now: ' + titleNode.textContent);
});

You have to use the Casper#evaluate() method in order to communicate with the page DOM:

// this will
casper.then(function() {
    var titleText = this.evaluate(function() {
        return document.querySelector('h1').textContent;
    });
    this.echo('Title is: ' + titleText);
    this.evaluate(function() {
        document.querySelector('h1').textContent = 'New title';
    });
    this.echo('Title is now: ' + this.evaluate(function() {
        return document.querySelector('h1').textContent;
    }));
});

Of course, it’s a whole lot more verbose, but Casper provides convenient methods to ease accessing elements properties, eg. Casper#fetchText() and Casper#getElementInfo():

// this will
casper.then(function() {
    this.echo('Title is: ' + this.fetchText('h1'));
    this.evaluate(function() {
        document.querySelector('h1').textContent = 'New title';
    });
    this.echo('Element HTML is now: ' + this.getElementInfo('h1').html);
});

Why can’t I create a new casper instance in a test environment?

The casperjs test subcommand is a convenient utility which bootstraps and configures a test environment for you, so a preconfigured casper object is already available in your test script when using this command.

As of 1.1-beta3, you’re prevented from overriding this preconfigured instance as this practice prevents the test runner from working properly. If you try to create a new casper instance in a test script, you’ll get an error and CasperJS will exit with an error message with a link pointing to the documentation.

One may argue this is mostly related to some historical bad design decisions, and this might be true. This behavior is not likely to exist anymore in a future 2.0.

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: