Your Form Is Not Portable If It Contains Callbacks

What makes a form portable? Not JSON alone. Its validation, conditions, collections and submission semantics must survive the trip too. I wrote about the architecture behind Modyra and the trade-offs involved. Your Form Is Not Portable If It Contains Callbacks Most form libraries help us manage forms inside an application. They track values, execute validators, expose errors and eventually produce a submission payload. That works well until the form needs to exist somewhere else. Perhaps its structure comes from a backend. Perhaps a visual builder generates it. Perhaps multiple applications must render it. Perhaps the server must independently validate the same conditional rules used by the browser. At that point, the form is no longer just component state. It is a contract. And most form abstractions cannot cross that boundary. The portability illusion Consider a typical conditional validator: const form = createForm ({ defaultValues : { country : ' IT ' , vatId : '' , }, validators : { onChange : ({ value }) => { if ( value . country === ' IT ' && ! value . vatId ) { return { fields : { vatId : ' VAT ID is required in Italy ' , }, }; } }, }, }); This is perfectly reasonable application code. It is also not portable. The callback cannot travel through an API as JSON. A Java service cannot execute it. A visual editor cannot reliably inspect it. Another runtime cannot reproduce its meaning without receiving executable source code. We can serialize the values around the callback, but not the behavior itself. This leads to an important distinction: A form configuration is not a portable form contract if part of its meaning still lives inside executable callbacks. The obvious shortcuts are dangerous There are several tempting ways to work around this limitation. Serialize the callback as source code { "condition" : "value.country === 'IT'" } The receiving application must now parse or execute an expression encoded as text. That creates immediate problems: the expression