Built-in types, validation constraints, showWhen operators, and $Infer mappings.

Seven built-in types in @dimah-form/core. Each one has a definition schema, a server validator, and an $Infer mapping.

Built-In Field Types Catalog

Type	Answer Type	Schema Constraints	Description
`text`	`string`	`minLength?: number` `maxLength?: number` `pattern?: string` (regex)	Single-line or multi-line text input. Validates length and regex pattern.
`number`	`number`	`min?: number` `max?: number` `integer?: boolean`	Numeric input. Validates minimum, maximum, and integer constraints.
`boolean`	`boolean`	—	Checkbox or toggle switch. Values are strictly `true` or `false`.
`select`	`string`	`options: SelectOption[]`	Single-choice dropdown or radio group. Answer must match an option `value`.
`multiSelect`	`string[]`	`options: SelectOption[]`	Multi-choice checkbox group or tag selector. Answer must be an array of valid option values without duplicates.
`email`	`string`	—	Email address input. Validates standard RFC 5322 email formatting.
`date`	`string`	`min?: string` (YYYY-MM-DD) `max?: string` (YYYY-MM-DD)	Calendar date in `YYYY-MM-DD` ISO format. Validates date boundaries.

Select Option Structure

Options passed to select or multiSelect fields follow this schema:

type SelectOption = {
  /** The persisted answer value (e.g., "us", "uk", "de") */
  value: string;

  /** Display label for the UI (defaults to value if omitted) */
  label?: string;

  /** Custom metadata for icons, descriptions, or badge tags */
  meta?: Record<string, unknown>;
};

Conditional Visibility (`showWhen`)

The showWhen property dynamically hides or shows fields based on the respondent's answers.

Automatic Cleanup: When a field is conditionally hidden, its answer is automatically stripped from the submitted response so outdated answers never persist to your database.

1. Leaf Conditions

`equals`

Matches when the target field's answer strictly equals the specified value:

{
  id: "githubHandle",
  type: "text",
  label: "GitHub Handle",
  showWhen: { field: "role", equals: "developer" },
}

`notEquals`

Matches when the target field's answer is not equal to the specified value:

{
  id: "reason",
  type: "text",
  label: "Reason for cancellation",
  showWhen: { field: "plan", notEquals: "free" },
}

`includes`

Matches when a multiSelect array answer contains the specified value:

{
  id: "reactExperience",
  type: "number",
  label: "Years of React Experience",
  showWhen: { field: "skills", includes: "react" },
}

2. Compound Conditions (`all` / `any`)

`all` (Logical AND)

Matches only when all nested conditions evaluate to true:

showWhen: {
  all: [
    { field: "department", equals: "engineering" },
    { field: "isLead", equals: true },
  ],
}

`any` (Logical OR)

Matches when at least one nested condition evaluates to true:

showWhen: {
  any: [
    { field: "country", equals: "US" },
    { field: "country", equals: "CA" },
  ],
}

Type Inference (`$Infer`) Mapping

When defining forms with defineForm(), TypeScript derives the answer type automatically:

lib/forms/example.ts

import { defineForm } from "@dimah-form/server";

export const exampleForm = defineForm({
  title: "Example",
  slug: "example",
  fields: [
    { id: "name", type: "text", required: true },
    { id: "age", type: "number" }, // Optional because required is omitted
    {
      id: "role",
      type: "select",
      required: true,
      options: [{ value: "admin" }, { value: "user" }],
    },
    {
      id: "tags",
      type: "multiSelect",
      options: [{ value: "frontend" }, { value: "backend" }],
    },
  ],
});

The resulting $Infer answer type is strictly typed:

type ExampleAnswers = Form["$Infer"]["answers"]["example"];

// Resolves to:
// {
//   name: string;
//   role: "admin" | "user";
//   age?: number;
//   tags?: ("frontend" | "backend")[];
// }

Next Steps

Custom Fields

Create custom validators and $Infer type mappings with defineFieldType.

Widgets

Render UI widgets for all 7 built-in field types.

Protocol

Inspect request and response payload schemas.

Field Types

Custom Fields

Widgets

Protocol

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