I'm using CasperJS to automate a series of clicks, completed forms, parsing data, etc through a website.
Casper seems to be organized into a list of preset steps in the form of then
statements (see their example here: http://casperjs.org/quickstart.html) but it's unclear what triggers the next statement to actually run.
For example, does then
wait for all pending requests to complete? Does injectJS
count as a pending request? What happens if I have a then
statement nested - chained to the end of an open
statement?
casper.thenOpen('http://example.com/list', function(){
casper.page.injectJs('/libs/jquery.js');
casper.evaluate(function(){
var id = jQuery("span:contains('"+itemName+"')").closest("tr").find("input:first").val();
casper.open("http://example.com/show/"+id); //what if 'then' was added here?
});
});
casper.then(function(){
//parse the 'show' page
});
I'm looking for a technical explanation of how the flow works in CasperJS. My specific problem is that my last then
statement (above) runs before my casper.open
statement & I don't know why.
then()
basically adds a new navigation step in a stack. A step is a javascript function which can do two different things:
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 called.
When you have defined your navigation steps, run()
executes them one by one sequentially:
casper.run();
Footnote: the callback/listener stuff is an implementation of the Promise pattern.