@musicayciencia globals are used when you need to share data between script processors - although David correctly suggests that this should be the last tool you pick for that as there are way better ways for cross-module communication by now. The callback of a single script processor share all the variables declared in the onInit callback.
Now about the non-deterministic issue: if you compile that script it won't cause an error, as the JS compiler cannot know whether the variable setGlobalVariable is a function that can be called - it might get assigned to something callable at some point so it stays put and doesn't complain. However when you play a note, then it's time to call this variable and that's where HISE realises that you can't execute the (empty) variable.
var callableAtSecondTime = undefined;
function onNoteOn()
{
callableAtSecondTime();
}
function onNoteOff()
{
callableAtSecondTime = function()
{
Console.print("Now I work");
};
}
This script will throw an error when you press the first note, but the first note off will then assign a function to the variable so subsequent notes will not raise the error but call the function. That example looks weird, but it's one of the more powerful features of JS (and HiseScript) to be able to reassign function slots to different functions like this so you can implement dynamic logic more easily.
