How to pass multiple comma separated values in a cell to a custom function?

Suppose, there are values such as 1,A, 2,B, 3,D in certain cells. My intention is to add 1,2,3 (LHS) separately and A,B,D (RHS) separately. To achieve that, I have written certain custom function in "App script":

function GetNumber (number, alphabet) { return number; }

Now, how can I pass 1,A to the GetNumber() as 2 arguments so that, the logic works?
I tried SPLIT, but it doesn't work:
=GetNumber(SPLIT(C1,",")) // C1 is a column cell

Though I am using Google sheet, MS-Excel equivalent may also help.