React Hook Form + Zod Validation

Status: Production Ready ✅ Last Updated: 2025-11-20 Dependencies: None (standalone) Latest Versions: [email protected], [email protected], @hookform/[email protected]

Quick Start (10 Minutes)

1. Install Packages

npm install [email protected] [email protected] @hookform/[email protected]

Why These Packages:

• react-hook-form: Performant, flexible form library with minimal re-renders
• zod: TypeScript-first schema validation with type inference
• @hookform/resolvers: Adapter to connect Zod (and other validators) to React Hook Form

2. Create Your First Form

import { useForm } from 'react-hook-form'
import { zodResolver } from '@hookform/resolvers/zod'
import { z } from 'zod'

// 1. Define validation schema
const loginSchema = z.object({
  email: z.string().email('Invalid email address'),
  password: z.string().min(8, 'Password must be at least 8 characters'),
})

// 2. Infer TypeScript type from schema
type LoginFormData = z.infer<typeof loginSchema>

function LoginForm() {
  // 3. Initialize form with zodResolver
  const {
    register,
    handleSubmit,
    formState: { errors, isSubmitting },
  } = useForm<LoginFormData>({
    resolver: zodResolver(loginSchema),
    defaultValues: {
      email: '',
      password: '',
    },
  })

  // 4. Handle form submission
  const onSubmit = async (data: LoginFormData) => {
    // Data is guaranteed to be valid here
    console.log('Valid data:', data)
    // Make API call, etc.
  }

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <div>
        <label htmlFor="email">Email</label>
        <input id="email" type="email" {...register('email')} />
        {errors.email && (
          <span role="alert" className="error">
            {errors.email.message}
          </span>
        )}
      </div>

      <div>
        <label htmlFor="password">Password</label>
        <input id="password" type="password" {...register('password')} />
        {errors.password && (
          <span role="alert" className="error">
            {errors.password.message}
          </span>
        )}
      </div>

      <button type="submit" disabled={isSubmitting}>
        {isSubmitting ? 'Logging in...' : 'Login'}
      </button>
    </form>
  )
}

CRITICAL:

• Always set defaultValues to prevent "uncontrolled to controlled" warnings
• Use zodResolver(schema) to connect Zod validation
• Type form with z.infer<typeof schema> for full type safety
• Validate on both client AND server (never trust client validation alone)

3. Add Server-Side Validation

// server/api/login.ts
import { z } from 'zod'

// SAME schema on server
const loginSchema = z.object({
  email: z.string().email('Invalid email address'),
  password: z.string().min(8, 'Password must be at least 8 characters'),
})

export async function loginHandler(req: Request) {
  try {
    // Parse and validate request body
    const data = loginSchema.parse(await req.json())

    // Data is type-safe and validated
    // Proceed with authentication logic
    return { success: true }
  } catch (error) {
    if (error instanceof z.ZodError) {
      // Return validation errors to client
      return { success: false, errors: error.flatten().fieldErrors }
    }
    throw error
  }
}

Why Server Validation:

• Client validation can be bypassed (inspect element, Postman, curl)
• Server validation is your security layer
• Same Zod schema = single source of truth
• Type safety across frontend and backend

Core Concepts

useForm Hook Anatomy

const {
  register,           // Register input fields
  handleSubmit,       // Wrap onSubmit handler
  watch,              // Watch field values
  formState,          // Form state (errors, isValid, isDirty, etc.)
  setValue,           // Set field value programmatically
  getValues,          // Get current form values
  reset,              // Reset form to defaults
  trigger,            // Trigger validation manually
  control,            // Control object for Controller/useController
} = useForm<FormData>({
  resolver: zodResolver(schema),  // Validation resolver
  mode: 'onSubmit',               // When to validate (onSubmit, onChange, onBlur, all)
  defaultValues: {},              // Initial values (REQUIRED for controlled inputs)
})

useForm Options:

Form Validation Modes:

• onSubmit - Validate on submit (best performance, less responsive)
• onChange - Validate on every change (live feedback, more re-renders)
• onBlur - Validate when field loses focus (good balance)
• all - Validate on submit, blur, and change (most responsive, highest cost)

Zod Schema Definition

import