How do we check for changes on File custom scripted field type? Here are the snippets from a Suitelet and ClientScript I am working on Suitelet - Add file field type

const fileFieldObj = assistantObject.addField({
    id: 'custpage_sample_file',
    label: 'Sample File',
    type: serverWidget.FieldType.FILE
});
fileFieldObj.setHelpText({
    help: 'The sample file to process.',
    showInlineForAssistant: false
});
fileFieldObj.isMandatory = true;

ClientScript - fieldChanged entry point

const { fieldId, currentRecord: curRec } = scriptContext;
console.log(`${fieldId} changed`);

I have another select field on this suitelet as well but it appears on the console while the file type field does not. Any ideas? I've also tried lookin on suiteanswers for clues and I came up short for now.