I want to add:
Openbullet does not run javascript on it's own!
It only** does the requests that you tell it to do as good as possible (while obeying to the basic standard, like having a Hosts Header)
And store the answer in the Variable <SOURCE> and as a extra service, it also automatically parses some stuff like Cookies, Headers, the Statuscode and so on to Varlables
But again, it DOES NOT run stuff like Javascript or so and do requests you haven't told it to do (beside follow redirects if you want)
So you have to tell it, what to do - it's your job to find things out like what some javascript is doing. - And replicate the stuff you need in OB.
If you want it to run javascript automatically, then use Selenium. - which comes with it's own tradeoffs.
**= this does not include selenium