Open the 'SAPMV45A.E0101.sjs' script file. Create this file if it does not already exist. All additions will be made to this file.
The default VA01 screen appears as follows:

Create a checkbox on the VA01 screen. The code is as follows:
checkbox([11,15], "Check 1", {"name":"z_chkbx1"});
The VA01 screen will now appear as shown below::
