How does CasperJs bind variables? - variables

Question

I have the following code which does not post data as expected
var casper = require('casper').create();
var myData;
var utils = require('utils');
casper.start();
casper.then(function () {
myData = {"source":"casperjs"};
utils.dump(myData);
});
casper.thenOpen('http://my-api/api/upload/', {
method: "post",
data: JSON.stringify(myData),
headers: {
"Content-Type":"application/json"
}
}, function () {
utils.dump(myData);
});
casper.run();
The message was sent to my server but without valid data. However, if I move the thenOpen(...) into the then(...) like this
casper.then(function () {
myData = {"source":"casperjs"};
utils.dump(myData);
this.thenOpen('http://my-api/api/upload/', {
method: "post",
data: JSON.stringify(myData),
headers: {
"Content-Type":"application/json"
}
}, function () {
utils.dump(myData);
});
});
Then the post would succeed. Or If i change the thenOpen part in the original code (i.e., without moving it in to the casper.then(...) part, like this
casper.thenOpen('http://my-api/api/upload/', {
method: "post",
data: JSON.stringify({"source":"casperjs"}),
headers: {
"Content-Type":"application/json"
}
}, function () {
utils.dump(myData);
});
Then the post would also be successful. So it looks like myData has to be initialized when the thenOpen(...) is seen. So is this expected or I have done something wrong? I could not find reference about this behavior. Thanks!

Answer 1

This is expected behavior as casperjs schedules the steps before running them. This means for your first listing that JSON.stringify(undefinded) will be sent to the server. The reason is that your first casper.then block was not yet executed when the object is evaluated for your casper.thenOpen block. Therefore your data was not yet assigned properly to myData, which happens inside the step.
The evaluation of the POST data on the other hand is done for the thenOpen call and not inside, so it is executed synchronously.
You already provided some good alternatives.