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Conditional logic is evaluated automatically by @osforms/react as the user fills out the form. Hidden fields are skipped in navigation and excluded from the submission payload.

​
Types

import type {
  ConditionalLogic,
  Condition,
  ConditionOperator,
} from '@osforms/react';

type ConditionOperator =
  | 'equals'
  | 'not_equals'
  | 'contains'
  | 'not_contains'
  | 'greater_than'
  | 'less_than'
  | 'is_empty'
  | 'is_not_empty';

interface Condition {
  fieldId: string;
  operator: ConditionOperator;
  value?: string | number; // not needed for is_empty / is_not_empty
}

interface ConditionalLogic {
  action: 'show' | 'hide';
  match: 'all' | 'any'; // AND vs OR
  conditions: Condition[];
}

​
Usage in FormField

import type { FormField } from '@osforms/react';

const followUpField: FormField = {
  id: 'feedback_details',
  type: 'textarea',
  label: 'Tell us more',
  required: false,
  conditionalLogic: {
    action: 'show',
    match: 'all',
    conditions: [{ fieldId: 'rating', operator: 'less_than', value: 3 }],
  },
};

​
How the SDK evaluates conditions

The @osforms/react SDK evaluates conditions in real time using the isFieldVisible utility: 
import { isFieldVisible, getVisibleFields } from '@osforms/react';
// Note: these utils are used internally by useFormState
Evaluation rules:
  • equals / not_equals — strict string comparison after coercion (String(value))
  • contains / not_contains — substring check on stringified value
  • greater_than / less_than — numeric comparison after Number() coercion
  • is_empty — undefined, null, or empty string
  • is_not_empty — any other value
  • match: 'all' — every condition must be true (AND)
  • match: 'any' — at least one condition must be true (OR)

​
Accessing visible fields

When using useFormState directly, visibleFields reflects the current set of visible fields after applying all conditional logic: 
import { useFormState, useFormSchema } from '@osforms/react';

const { schema } = useFormSchema('form-slug');
const [state, actions] = useFormState(schema, endpoint);

// actions.visibleFields — fields visible based on current answers
// actions.currentField  — the field at state.currentIndex
Hidden fields are automatically filtered out of visibleFields and are not included in the submission payload. For full conditional logic documentation, see Core / Conditional Logic.