Inside function node's code the general lua rules apply: https://www.lua.org/pil/4.2.html
In LuvitRED there is an additional way to use global or flow wide variables. Using this method a variable can be accessed from within every function node.
By using the prefix global, the variable will be stored in RAM with the key following the prefix (separated by a . ). This method is identical to using the 'global store' node to store a variable to RAM, and both can be used together.
function block 1 global.variable = msg.payload return function block 2 if global.variable ~= nil then msg.payload = global.variable return msg
The attached flow demonstrates the use of the multiple ways to store/retrieve variables in LuvitRED.