A JSFunction can not be linked to a MappingRule. As all JSRunnable,
this Rhapsody Function must be implemented in JavaScript via the "Implementation" tab:
The implemented code have access to all of the M2MRuleset JavaScript context (including init.js, JSRunnables, JSFunctions, JSVariables, JSFileLibraryies).
The function signature is free, all needed arguments can be added, and it can return any variables.
This function can be called everywhere from the M2MRuleset JavaScript context.