Core Best Practices

Keep policies small

Prefer one policy per form section or domain concept. A checkout flow might use CustomerPolicy, ShippingPolicy, BillingPolicy, and PaymentPolicy.

Use stable paths

Paths are the contract between policy and UI.

helper.validateFor('addresses.0.city').isRequired('City is required');

For dynamic arrays, regenerate the policy when the array shape changes.

Pair required and format rules

helper.validateFor('email')
  .isRequired('Email is required')
  .isEmail('Enter a valid email address');

Without isRequired, an empty email is valid because the format rule is optional.

Avoid UI work in Core

Do not put focus management, CSS class decisions, DOM queries, or framework state updates in Core policies.

Test policy boundaries

Test empty required fields, invalid optional fields when populated, conditional dependencies, dynamic fields after add/remove, and a fully valid model.