Personas: Is Personas 100% compatible with Javascript?

Hi Personas experts,

In a ScriptButton, one can write JS codes in "Calculate in Javascript" tag.

I am wondering if I can write any JS codes here? What is the limit of JS codes that Personas does not support.

Another example issue is how the scope of a so-called "global variable" is inside Personas. Inside a Scriptbutton, one can use "args.myVar" to refer to a "global var" "myVar" through the actions in teh same button. But when refering to this var from other Scriptbutton, it seems that .myVar is not defined. Why?

Thanks.

Dong Zhu