As there are probably more ways to make a cookie in JavaScript can we all care to think about, other than by somehow 'running' the JavaScript, it will be impossible to know

1. if there is a cookie;
2. what the content of the cookie is.

This means that you must execute all JavaScript code on the webpage, to be sure that the correct value of the cookie is calculated.

CountZero

"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law