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I am attempting the following: parse a series of sequential URLs using CasperJS.

What I want to do in this example:

CasperJS should open "example.com/page-1.html", then "example.com/page-2.html", then "example.com/page-3.html".

My approach is to use a while loop. The problem is that casper.thenOpen is running the while loop at a different "speed", and casper.thenOpen seems to execute after the loop has finished. See it for yourself:

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

casper.start();

casper.then(function() {

    var current = 1;
    var end = 3;

    while(current <= end) {

          casper.echo('casper.echo: '+current);

          casper.thenOpen('http://example.com/page-' + current +'.html', function() {
                        this.echo('casper.thenOpen: '+current);

          });

          var current = current + 1;

    } // end while

}); // end casper.then

casper.run(function() {
    this.echo('Done.').exit();
});

The output: 

casper.echo: 1
casper.echo: 2
casper.echo: 3
casper.thenOpen: 4
casper.thenOpen: 4
casper.thenOpen: 4
Done.

I don't understand the logic. The while loop seems to run properly, since the "casper.echo" is counting correctly from 1 to 3. What bugs me is that the "casper.thenOpen" output is occurring after the loop is finished, since the value is 4.

In practical use, this code would open three times the page "example.com/page-4.html", instead of the ones we're expecting.

Why is this happening, and what would be the correct approach?

Manu
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    `casper.thenOpen()` is asynchronous and the steps are executed after the loop is completed. – Artjom B. Feb 15 '15 at 10:58
  • Thanks for the answers. So actually there are two things to keep in mind: 1: closures and function scope, 2: casper.thenOpen() being asynchronous. Still not sure how this knowledge leads to a solution regarding the asynchronicity. – Manu Feb 16 '15 at 15:33
  • You have to think about what value `current` has. The first `thenOpen` will be executed after the `while` loop finished every iteration. So the `current` in the `then` function of `thenOpen` points to `current` from the last iteration. – Artjom B. Feb 16 '15 at 15:40
  • Great, I got a working solution ! Finally I used a `for` loop and applied the simple asynchronous method found in this answer: http://stackoverflow.com/a/11488129/1904769 – Manu Feb 16 '15 at 23:02

0 Answers0