Gettind data from Timesheet using client script

I have the following code, which returns the field that triggers a changeField event. It works on a Job record type, but it doesn't work on a TimeSheet type. I am simply trying to show/hide a field based on the Customer a user chooses when adding time to a timesheet.

EXAMPLE:

 define(['N/currentRecord'], function () {        function fieldChanged(context) {        //context.fieldId returns the proper id in all cases        //getField() only works on the Job record type, returns null on Timesheet grid            var f = context.currentRecord.getField({fieldId: context.fieldId});              f.isDisplay = false;      }        return {          fieldChanged: fieldChanged      }    }  ); 

Can anyone point me in the right direction? Is there another way I am supposed to get the field and its value for a Timesheet grid? getField is supposed to work but it doesn't. If I pass it any field Id in the grid it returns null.