Can I scrape data from web pages when the data comes from JavaScript?
Although your question isn't very clear. I'm guessing that you are trying to access the javascript console. 
In Google Chrome: 

Press F12
Go to the 'console' tab 

In Mozilla Firefox with Firebug installed:

Open Firebug
Go to the 'console' tab

From the console you can execute javascript query's (calling functions, accessing variables etc.).
I hope this answered your question properly.
I'm not exactly sure how to phrase my question but I'll give it my best shot.
If I load up a webpage, in the HTML it executes a JavaScript file.  And if I view the page source I can see the source of that JavaScript (though it's not very well formatted and hard to understand).
Is there a way to run the JavaScript from e.g. Python code, without going through the browser?  i.e if I wanted to access a particular function in that JavaScript, is there a clean way to call just that from a Python script, and read the results?
For example... a webpage displays a number that I want access to.  It's not in the page source because it's a result from a JavaScript call.  Is there a way to call that JavaScript from Python?