extending.rst 3.74 KB

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Extending
Sometimes it can be convenient to add your own methods to a Casper object instance; you can easily do so as illustrated in the example below:
var casper = require('casper').create({
    verbose: true,
    logLevel: "debug"
});

var links = {
    'http://edition.cnn.com/': 0,
    'http://www.nytimes.com/': 0,
    'http://www.bbc.co.uk/': 0,
    'http://www.guardian.co.uk/': 0
};

casper.countLinks = function() {
    return this.evaluate(function() {
        return __utils__.findAll('a[href]').length;
    });
};

casper.renderJSON = function(what) {
    return this.echo(JSON.stringify(what, null, '  '));
};

casper.start();

casper.each(Object.keys(links), function(casper, link) {
    this.thenOpen(link, function() {
        links[link] = this.countLinks();
    });
});

casper.run(function() {
    this.renderJSON(links).exit();
});

But that's just plain old monkey-patching the casper object, and you may probably want a more OO approach… That's where the inherits() function from the utils module and ported from nodejs comes handy:
var Casper = require('casper').Casper;
var utils = require('utils');
var links = {
    'http://edition.cnn.com/': 0,
    'http://www.nytimes.com/': 0,
    'http://www.bbc.co.uk/': 0,
    'http://www.guardian.co.uk/': 0
};

function Fantomas() {
    Fantomas.super_.apply(this, arguments);
}

// Let's make our Fantomas class extending the Casper one
// please note that at this point, CHILD CLASS PROTOTYPE WILL BE OVERRIDEN
utils.inherits(Fantomas, Casper);

Fantomas.prototype.countLinks = function() {
    return this.evaluate(function() {
        return __utils__.findAll('a[href]').length;
    });
};

Fantomas.prototype.renderJSON = function(what) {
    return this.echo(JSON.stringify(what, null, '  '));
};

var fantomas = new Fantomas({
    verbose: true,
    logLevel: "debug"
});

fantomas.start();

Object.keys(links).forEach(function(url) {
    fantomas.thenOpen(url, function() {
        links[url] = this.countLinks();
    });
});

fantomas.run(function() {
    this.renderJSON(links).exit();
});


Note
The use of the super_ child class property which becomes available once its parent has been defined using inherits(); it contains a reference to the parent constructor.
Don't forget to call ``Casper``'s parent constructor!
Of course this approach is bit more verbose than the easy monkey-patching one, so please ensure you're not just overengineering stuff by subclassing the Casper class.


Using CoffeeScript
If you're writing your casper scripts using CoffeeScript, extending casper is getting a bit more straightforward:
links =
    'http://edition.cnn.com/': 0
    'http://www.nytimes.com/': 0
    'http://www.bbc.co.uk/': 0
    'http://www.guardian.co.uk/': 0

class Fantomas extends require('casper').Casper
    countLinks: ->
        @evaluate ->
            __utils__.findAll('a').length

    renderJSON: (what) ->
        @echo JSON.stringify what, null, '  '

fantomas = new Fantomas
    loadImages:  false
    logLevel:    "debug"
    verbose:     true

fantomas.start()

for url of links
    do (url) ->
        fantomas.thenOpen url, ->
            links[url] = @countLinks()

fantomas.run ->
    @renderJSON links
    @exit()