fusengine/nextjs-tanstack-form

TanStack Form for Next.js 16

Type-safe, performant forms with Server Actions and signal-based reactivity.

Agent Workflow (MANDATORY)

Before ANY implementation, use TeamCreate to spawn 3 agents:

1. fuse-ai-pilot:explore-codebase - Analyze existing forms and validation patterns
2. fuse-ai-pilot:research-expert - Verify latest TanStack Form docs via Context7/Exa
3. mcp__context7__query-docs - Check form options and field API

After implementation, run fuse-ai-pilot:sniper for validation.

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Overview

When to Use

• Building forms with complex validation requirements
• Need Server Actions integration for form submission
• Implementing multi-step wizards or dynamic field arrays
• Require real-time async validation (username availability)
• Want type-safe forms with full TypeScript inference

Why TanStack Form

| Feature | Benefit | |---------|---------| | Signal-based state | Minimal re-renders, optimal performance | | Full TypeScript | DeepKeys, DeepValue inference | | Server Actions native | Built-in Next.js 16 integration | | Zod adapter | Schema-first validation | | Framework agnostic | Same API for React, Vue, Solid | | Headless | Works with any UI library (shadcn/ui) |

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Critical Rules

1. formOptions shared - Define once, use in client and server
2. Server validation - DB checks in onServerValidate, not client
3. Zod schemas - Client-side instant feedback
4. useActionState - React 19 hook for Server Actions
5. mergeForm - Combine server errors with client state
6. SOLID paths - Forms in modules/[feature]/src/components/forms/

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SOLID Architecture

Module Structure

Forms organized by feature module:

• modules/auth/src/components/forms/ - Auth forms (login, signup)
• modules/auth/src/interfaces/ - Form types and schemas
• modules/auth/src/actions/ - Server Actions for form submission
• modules/cores/lib/forms/ - Shared form utilities

File Organization

| File | Purpose | Max Lines | |------|---------|-----------| | form-options.ts | Shared formOptions + Zod schema | 50 | | FormComponent.tsx | Client form UI with fields | 80 | | form.action.ts | Server Action with validation | 30 | | form.interface.ts | Types for form values | 30 |

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Key Concepts

Form Options Pattern

Define form configuration once, share between client and server. Ensures type safety and consistency.

Field API

Each field has state (value, errors, touched, validating) and handlers (handleChange, handleBlur).

Validation Levels

• onChange - Real-time as user types
• onBlur - When field loses focus
• onSubmit - Before form submission
• onServer - Server-side in action

Error Management

Errors exist at field-level and form-level. Use field.state.meta.errors for field errors, form.state.errorMap for form errors.

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Reference Guide

| Need | Reference | |------|-----------| | Initial setup | installation.md | | Basic patterns | basic-usage.md, field-api.md | | Validation | validation-zod.md, async-validation.md | | Server Actions | server-actions.md | | Dynamic forms | array-fields.md, multi-step-form.md | | UI integration | shadcn-integration.md | | TypeScript | typescript.md | | Migration | migration-rhf.md | | Client-side form component | client-form.md — load when wiring useActionState + mergeForm in a 'use client' form component | | Server-side validation | server-validation.md — load when writing createServerValidate + ServerValidateError in a Server Action |

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Best Practices

1. Define schemas first - Zod schemas drive both validation and types
2. Shared formOptions - Single source of truth for client/server
3. Debounce async validation - Use asyncDebounceMs for API calls
4. form.Subscribe - Selective re-renders for submit state
5. Field composition - Reusable field components with shadcn/ui
6. Server errors merge - Use mergeForm to show server validation errors

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Comparison vs React Hook Form

| Aspect | TanStack Form | React Hook Form | |--------|---------------|-----------------| | Type Safety | 100% (DeepKeys) | Manual typing | | Performance | Signals (minimal) | Refs (good) | | Server Actions | Native support | Manual integration | | Bundle Size | ~12KB | ~9KB | | Learning Curve | Medium | Low | | Use Case | Complex apps | Standard forms |