Conditional Logic

Forma uses FEEL expressions to control dynamic field behavior. Three properties control when fields are visible, required, or editable.

Properties

Property	Description	Default
visibleWhen	Show field when expression is true	Always visible
requiredWhen	Require field when expression is true	Uses schema required
enabledWhen	Allow editing when expression is true	Always enabled
readonlyWhen	Make field read-only when expression is true	Always editable

visibleWhen

Control when a field is displayed:

{
  "dependentField": {
    "label": "Dependent Field",
    "visibleWhen": "triggerField = true"
  }
}

Examples

Show based on checkbox:

{
  "visibleWhen": "hasInsurance = true"
}

Show based on selection:

{
  "visibleWhen": "country = \"US\""
}

Show based on number:

{
  "visibleWhen": "age >= 18"
}

Show based on multiple conditions:

{
  "visibleWhen": "hasInsurance = true and insuranceType = \"health\""
}

Hidden Field Behavior

• Hidden fields are not validated
• Hidden fields retain their values (not cleared)
• Hidden fields are excluded from submission if not visible

requiredWhen

Make a field conditionally required:

{
  "insuranceNumber": {
    "label": "Insurance Number",
    "visibleWhen": "hasInsurance = true",
    "requiredWhen": "hasInsurance = true"
  }
}

Priority

• requiredWhen overrides the schema's required array
• If both schema required and requiredWhen are set, requiredWhen takes precedence

Examples

Required based on selection:

{
  "requiredWhen": "paymentMethod = \"credit_card\""
}

Required based on checkbox:

{
  "requiredWhen": "needsShipping = true"
}

enabledWhen

Control when a field can be edited:

{
  "approvedBy": {
    "label": "Approved By",
    "enabledWhen": "status = \"pending\""
  }
}

Disabled fields:

• Are visible but grayed out
• Cannot be edited by the user
• Retain their existing value

Examples

Disable after submission:

{
  "enabledWhen": "submissionStatus != \"submitted\""
}

Enable only for specific users:

{
  "enabledWhen": "userRole = \"admin\""
}

readonlyWhen

Make a field conditionally read-only:

{
  "invoiceNumber": {
    "label": "Invoice Number",
    "readonlyWhen": "status = \"approved\""
  }
}

Readonly fields differ from disabled fields (enabledWhen: false):

• Readonly: Visible and focusable, values are submitted, but the field cannot be edited
• Disabled: Field appears greyed out and cannot be interacted with

Examples

Read-only after approval:

{
  "readonlyWhen": "approvalStatus = \"approved\""
}

Read-only for non-admins:

{
  "readonlyWhen": "userRole != \"admin\""
}

FEEL Expression Syntax

Comparison Operators

Operator	Description	Example
=	Equal	status = "active"
!=	Not equal	status != "archived"
>	Greater than	age > 18
>=	Greater or equal	age >= 21
<	Less than	price < 100
<=	Less or equal	price <= 50

Logical Operators

Operator	Description	Example
and	Both conditions true	age >= 18 and hasLicense = true
or	Either condition true	status = "active" or status = "pending"
not	Negation	not(isBlocked)

String Values

Strings must be quoted with escaped quotes:

{
  "visibleWhen": "country = \"US\""
}

Null Checks

{
  "visibleWhen": "email != null"
}

Referencing Other Fields

Reference fields directly by name:

{
  "visibleWhen": "firstName != null and lastName != null"
}

Referencing Computed Values

Use the computed. prefix:

{
  "visibleWhen": "computed.total > 1000"
}

Common Patterns

Show Additional Fields

{
  "otherReason": {
    "label": "Please specify",
    "visibleWhen": "reason = \"other\""
  }
}

Conditional Sections

Group related fields with the same condition:

{
  "companyName": {
    "label": "Company Name",
    "visibleWhen": "customerType = \"business\""
  },
  "taxId": {
    "label": "Tax ID",
    "visibleWhen": "customerType = \"business\""
  }
}

Progressive Disclosure

Reveal fields as users complete previous ones:

{
  "step2Field": {
    "visibleWhen": "step1Field != null"
  },
  "step3Field": {
    "visibleWhen": "step2Field != null"
  }
}

Mutual Exclusion

Show one field OR another:

{
  "phoneNumber": {
    "visibleWhen": "contactMethod = \"phone\""
  },
  "emailAddress": {
    "visibleWhen": "contactMethod = \"email\""
  }
}