function fieldChanged(scriptContext) {
    	var currentRecord = scriptContext.currentRecord;
    	if (scriptContext.fieldId === 'custrecord_itemsupplier_suppliercode') {
    		function changeToCaps(scriptContext) {
    			var preCaps = currentRecord.getValue({fieldId: 'custrecord_itemsupplier_suppliercode'});
    			var afterCaps = preCaps.toUpperCase();
    			currentRecord.setValue({fieldId:'custrecord_itemsupplier_suppliercode', value: afterCaps});
    		}
    		changeToCaps(scriptContext);
    	}
    }

Looks like this now.