Conditional Logic

import { when } from '@intentform/core'

const accidentReportModel = {
  // ...
  rules: [
    when('injuryType', 'severe').show('hospitalName'),
    when('injuryType', 'severe').require('hospitalName'),
    when('consent', false).hide('signatureDate'),
    when('injuryType', 'none').disable('treatmentReceived'),
  ],
}

Available actions

Method	Effect
`.show(field)`	Make the field visible (hidden by default if this rule exists)
`.hide(field)`	Hide the field
`.require(field)`	Mark the field as required
`.disable(field)`	Render the field but prevent editing

Multiple conditions, multiple effects

Chain multiple rules targeting the same field:

rules: [
  when('travelClass', 'business').show('loyaltyNumber'),
  when('travelClass', 'first').show('loyaltyNumber'),
  when('hasInsurance', true).show('policyNumber'),
  when('hasInsurance', true).require('policyNumber'),
]

Rule evaluation

Rules are evaluated by evaluateRules(rules, values) from @intentform/core. The function returns a map of field names to their current state:

import { evaluateRules } from '@intentform/core'

const state = evaluateRules(model.rules, currentValues)
// state.hospitalName → { visible: true, required: true, disabled: false }

The engine re-runs evaluateRules on every field change, so visibility updates instantly as the user fills the form.

Default visibility

If no .show() or .hide() rule targets a field, that field is visible by default. A field only becomes hidden by default when at least one .show() rule references it — meaning “show only when condition is met.”

// hospitalName is hidden unless injuryType === 'severe'
when('injuryType', 'severe').show('hospitalName')