Google Sheets Script

[PC User]

I was looking for a way to adapt an Excel VBA script to work on Google Sheets, but I cannot find any explanation about how to do this. Where can I find that information. Here is the VBA script that I'm trying to convert.

Function Numerology(WhatDate As Variant) As Long
Dim lngLoop As Long
Dim lngSum As Long
Dim strNumber As String
 
    strNumber = Format(WhatDate, "yyyymmdd")
    Do While Len(strNumber) > 1
        lngSum = 0
        For lngLoop = 1 To Len(strNumber)
            lngSum = lngSum + CLng(Mid(strNumber, lngLoop, 1))
        Next lngLoop
        strNumber = CStr(lngSum)
    Loop
    
    Numerology = lngSum
    
End Function