CODEWITHSUNDEEP
javascriptphantomjs
dthree
dthree

Reputation: 20790

Casper - understanding evaluate with function callbacks

This is a bit of a tricky question.

I am very familiar with javascript, however I am on a project that auto-crawls a website using PhantomJS and CasperJS. These are entirely new subjects to me.

I was able to figure out how to use Casper and navigate, log in to pages, etc, however it is unweildy as the general flow seems to be:

casper.start('http://google.fr/');

casper.then(function() {
    this.echo("I'm in your google.");
});

casper.then(function() {
    this.echo('Now, let me write something');
});

casper.then(function() {
    this.echo('Oh well.');
});

casper.run();

My problem with this is that I want to do all sorts of things with the website, depending on what data is gotten with it. I can't pre-layout the sequence of navigations and not have it change. I hope this makes sense.

To solve this, I created a Javascript Navigator object with builtin functions. My general concept was:

navigator.logIn(function() 
{
  navigator.actionA(parameters, function() 
  {
    if (navigator.data.a == navigator.data.b) {
      navigator.actionB();
    } else {
      navigator.actionC();
    }
  });
});

And embedded in each of these functions would be casper functions.

Here is a shortened version of my actual code, and where things started getting funky:

var casper = require('casper').create({
    clientScripts:  [ 'jquery.min.js' ],
    onError: function(self, m) {  
        console.log('FATAL:' + m);
        self.exit();              
    },
});

var navigator = new _Navigator();

function _Navigator() { }

_Navigator.prototype.logIn = function(aCallback)
{
  var self = this;

  casper.start('https://website/login.asp', function() 
  {
    if (1 == 1) {
      this.evaluate(function() {
        $("input[name=blah]").val('blahblah');
      });

      // ... A LOT MORE CODE
      aCallback();
    }
  });  
}

_Navigator.prototype.search = function(aDataSet, aCallback)
{
  var self = this;

  console.log('this works');
  casper.then(function(){
    console.log('this works');
  });

  var firstName = 'foobar';

  casper.then(function(){
    console.log('this works');
    this.evaluate(function()
    {
      console.log('this no longer works!!');
      $('input[id=blah]').val(firstName);
      aCallback();
    });
  });
}

navigator.logIn(function() {
  // LOG IN RUNS, AND CALLS BACK SUCCESSFULLY...
  navigator.search({'dataset'}, function() 
  {
    console.log('This never runs');
  });
});

casper.run();

You'll notice that in the navigator.login function, I call casper.start(); In this, the evaluation function works fine, however then I do a callback function within that casper.start(); In my callback, I call the next function, navigator.search, which I suppose is still technically executing in the casper.start?

When I try running casper.evaluate within this new function called by the first callback function, everything seems to behave fine with the exception that casper.evaluate no longer works! It seems to eat the function, not printing any console logs or anything.

I have tried everything on this. I am not sure how to do this correctly. Does anyone have any suggestions on what I am doing wrong? Thanks.

Upvotes: 3

Views: 1614

Answers (2)

Mark Simon
Mark Simon

Reputation: 762

casper.evaluate() is as a window onto the headless browser session. Anything that happens in functions passed to evaluate doesn't appear on your local console. However, you can either log any value returned from evaluate or print all output by setting up a listener:

  casper.on('remote.message', function(message) {
    console.log(message);
  });

Upvotes: 0

nrabinowitz
nrabinowitz

Reputation: 55678

I know this is quite old, but: What's going on here is a combination of two issues:

  • casper.evaluate() seems to eat all errors within the current stack - onError won't run from inside an .evaluate() callback.

  • Functions used in .evaluate are not standard closures - they're sandboxed, and have no access to variables outside their scope, unless passed as explicit arguments to casper.evaluate. So in the evaluated function where you call aCallback() there's no aCallback in scope, and the function will fail (silently) with a ReferenceError.

Upvotes: 4

Related Questions