react-forms

React Forms

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: react topic: forms for comprehensive documentation on React form patterns and validation strategies.

Full Reference: See advanced.md for Server Actions, Multi-Step Forms, Dependent Fields, Auto-Save, Validation Patterns, and Accessibility.

Controlled vs Uncontrolled

Controlled Forms

React state controls the input:

function ControlledForm() {
  const [formData, setFormData] = useState({
    email: '',
    password: '',
  });
  const [errors, setErrors] = useState<Record<string, string>>({});

  const handleChange = (e: React.ChangeEvent<HTMLInputElement>) => {
    const { name, value } = e.target;
    setFormData(prev => ({ ...prev, [name]: value }));

    if (errors[name]) {
      setErrors(prev => ({ ...prev, [name]: '' }));
    }
  };

  const handleSubmit = (e: React.FormEvent) => {
    e.preventDefault();

    const newErrors: Record<string, string> = {};
    if (!formData.email) newErrors.email = 'Email required';
    if (!formData.password) newErrors.password = 'Password required';

    if (Object.keys(newErrors).length > 0) {
      setErrors(newErrors);
      return;
    }

    console.log('Submitting:', formData);
  };

  return (
    <form onSubmit={handleSubmit}>
      <div>
        <input
          name="email"
          type="email"
          value={formData.email}
          onChange={handleChange}
        />
        {errors.email && <span className="error">{errors.email}</span>}
      </div>

      <div>
        <input
          name="password"
          type="password"
          value={formData.password}
          onChange={handleChange}
        />
        {errors.password && <span className="error">{errors.password}</span>}
      </div>

      <button type="submit">Submit</button>
    </form>
  );
}

Uncontrolled Forms (useRef)

DOM controls the input:

function UncontrolledForm() {
  const emailRef = useRef<HTMLInputElement>(null);
  const passwordRef = useRef<HTMLInputElement>(null);

  const handleSubmit = (e: React.FormEvent) => {
    e.preventDefault();

    const data = {
      email: emailRef.current?.value,
      password: passwordRef.current?.value,
    };

    console.log('Submitting:', data);
  };

  return (
    <form onSubmit={handleSubmit}>
      <input ref={emailRef} name="email" type="email" />
      <input ref={passwordRef} name="password" type="password" />
      <button type="submit">Submit</button>
    </form>
  );
}

FormData API (Uncontrolled)

function FormDataForm() {
  const handleSubmit = (e: React.FormEvent<HTMLFormElement>) => {
    e.preventDefault();
    const formData = new FormData(e.currentTarget);

    const data = {
      email: formData.get('email') as string,
      password: formData.get('password') as string,
    };

    console.log('Submitting:', data);
  };

  return (
    <form onSubmit={handleSubmit}>
      <input name="email" type="email" required />
      <input name="password" type="password" required />
      <button type="submit">Submit</button>
    </form>
  );
}

---

React Hook Form

Most popular form library - uncontrolled with great DX:

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

const schema = z.object({
  email: z.string().email('Invalid email'),
  password: z.string().min(8, 'Password must be at least 8 characters'),
  confirmPassword: z.string(),
}).refine(data => data.password === data.confirmPassword, {
  message: 'Passwords must match',
  path: ['confirmPassword'],
});

type FormData = z.infer<typeof schema>;

function SignUpForm() {
  const {
    register,
    handleSubmit,
    formState: { errors, isSubmitting },
    reset,
  } = useForm<FormData>({
    resolver: zodResolver(schema),
    defaultValues: { email: '', password: '', confirmPassword: '' },
  });

  const onSubmit = async (data: FormData) => {
    try {
      await signUp(data);
      reset();
    } catch (error) {
      console.error('Sign up failed:', error);
    }
  };

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

      <div>
        <input {...register('password')} type="password" placeholder="Password" />
        {errors.password && <span className="error">{errors.password.message}</span>}
      </div>

      <div>
        <input {...register('confirmPassword')} type="password" placeholder="Confirm Password" />
        {errors.confirmPassword && <span className="error">{errors.confirmPassword.message}</span>}
      </div>

      <button type="submit" disabled={isSubmitting}>
        {isSubmitting ? 'Signing up...' : 'Sign Up'}
      </button>
    </form>
  );
}

Form Arrays

import { useFieldArray, useForm } from 'react-hook-form';

interface OrderForm {
  items: { productId: string; quantity: number }[];
  notes: string;
}

function OrderForm() {
  const { register, control, handleSubmit } = useForm<OrderForm>({
    defaultValues: {
      items: [{ productId: '', quantity: 1 }],
      notes: '',
    },
  });

  const { fields, append, remove } = useFieldArray({
    control,
    name: 'items',
  });

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      {fields.map((field, index) => (
        <div key={field.id} className="flex gap-2">
          <select {...register(`items.${index}.productId`)}>
            <option value="">Select product</option>
            {products.map(p => (
              <option key={p.id} value={p.id}>{p.name}</option>
            ))}
          </select>

          <input
            {...register(`items.${index}.quantity`, { valueAsNumber: true })}
            type="number"
            min="1"
          />

          <button type="button" onClick={() => remove(index)}>
            Remove
          </button>
        </div>
      ))}

      <button type="button" onClick={() => append({ productId: '', quantity: 1 })}>
        Add Item
      </button>

      <textarea {...register('notes')} placeholder="Notes" />
      <button type="submit">Submit Order</button>
    </form>
  );
}

Controlled Components with RHF

import { Controller, useForm } from 'react-hook-form';
import { DatePicker } from '@/components/date-picker';

function EventForm() {
  const { control, handleSubmit } = useForm();

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <Controller
        name="date"
        control={control}
        rules={{ required: 'Date is required' }}
        render={({ field, fieldState }) => (
          <div>
            <DatePicker
              value={field.value}
              onChange={field.onChange}
            />
            {fieldState.error && (
              <span className="error">{fieldState.error.message}</span>
            )}
          </div>
        )}
      />

      <button type="submit">Create Event</button>
    </form>
  );
}

---

Best Practices

Do	Don't
Use React Hook Form for complex forms	Manage all form state manually
Use Zod/Yup for validation	Write validation from scratch
Show inline errors	Show all errors at once
Use aria-* attributes	Forget accessibility
Debounce expensive validations	Validate async on every keystroke

• ✅ Use controlled inputs when you need real-time validation
• ✅ Use uncontrolled inputs (RHF) for better performance
• ✅ Validate on blur for better UX
• ✅ Show loading state during submission
• ❌ Don't disable submit button on empty form
• ❌ Don't clear form on error
• ❌ Don't show errors before user interaction

When NOT to Use This Skill

• React Hook Form with Zod schemas - Use react-hook-form skill for detailed patterns
• React 19 Server Actions forms - Use react-19 skill for useActionState and useFormStatus
• Simple input handling - Use react skill for basic controlled/uncontrolled inputs
• Form libraries other than RHF - Follow library-specific documentation

Anti-Patterns

Anti-Pattern	Problem	Solution
Managing all form state manually	Boilerplate, bugs	Use React Hook Form
Not validating user input	Security/UX issues	Use Zod validation schema
Showing all errors on mount	Bad UX	Validate on blur or submit
Disabling submit on empty form	Prevents validation messages	Allow submit, show errors
Clearing form on validation error	User loses data	Keep form data, show errors
Not showing loading state	Confusing UX	Show loading during submission
Missing accessibility attributes	Not accessible	Add aria labels and roles
Validating async on every keystroke	Performance issues	Debounce async validation

Quick Troubleshooting

Issue	Likely Cause	Fix
Form not submitting	Missing onSubmit or action	Add onSubmit handler to form
Validation not working	Schema not applied	Check resolver in useForm
Input not updating	Not controlled properly	Ensure value and onChange are set
Errors not showing	Missing FormMessage	Add FormMessage component
Submit button always disabled	Wrong isPending check	Use formState.isSubmitting
Values not resetting	Not calling reset()	Call form.reset() after success
Async validation too frequent	No debounce	Debounce validation function

Reference Documentation

• React Hook Form
• Zod
• MCP: mcp__documentation__fetch_docs → technology: react, topic: forms