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. 


example:

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.