/**
Ensure a function is only called once. When called multiple times it will return the return value from the first call.
@param fn - Function that should only be called once.
@returns A function that only calls `fn` once.
/**
Ensure a function is only called once. When called multiple times it will return the return value from the first call.
@param fn - Function that should only be called once.
@returns A function that only calls `fn` once.