Form Counter

[cdw0308]

I have an access database program that uses this code to put a number on the form based on what the last form number was.
It happen when the form loads. I am rewriting the program to be web-based. I need to know how to do the following in javascript.

Private Sub Form_Current()
 
 If Me.NewRecord Then
    On Error Resume Next 'It should never occur, just to be sure...
    Me!tran_ID.DefaultValue = Nz(DMax("[tran_ID]", "delivery"), 0) + 1
    
  End If
End Sub

Any help is appreciated.