React form handling with controlled components

Need patterns for handling forms in React: controlled inputs, validation, multi-field forms, and submission.

React form patterns:

import { useState, useCallback } from 'react';

// 1. Single controlled input
function SearchBox() {
  const [query, setQuery] = useState('');
  return (
    <input
      value={query}
      onChange={e => setQuery(e.target.value)}
      placeholder="Search..."
    />
  );
}

// 2. Multi-field form with single state object
function SignupForm() {
  const [form, setForm] = useState({
    name: '',
    email: '',
    password: '',
  });
  const [errors, setErrors] = useState({});

  const handleChange = useCallback((e) => {
    const { name, value } = e.target;
    setForm(prev => ({ ...prev, [name]: value }));
    // Clear error on change
    setErrors(prev => ({ ...prev, [name]: '' }));
  }, []);

  const validate = () => {
    const newErrors = {};
    if (!form.name.trim()) newErrors.name = 'Name is required';
    if (!form.email.includes('@')) newErrors.email = 'Invalid email';
    if (form.password.length < 8) newErrors.password = 'Min 8 characters';
    setErrors(newErrors);
    return Object.keys(newErrors).length === 0;
  };

  const handleSubmit = async (e) => {
    e.preventDefault();
    if (!validate()) return;
    // Submit form data
    await api.signup(form);
  };

  return (
    <form onSubmit={handleSubmit}>
      <div>
        <input name="name" value={form.name} onChange={handleChange} />
        {errors.name && <span className="error">{errors.name}</span>}
      </div>
      <div>
        <input name="email" type="email" value={form.email} onChange={handleChange} />
        {errors.email && <span className="error">{errors.email}</span>}
      </div>
      <div>
        <input name="password" type="password" value={form.password} onChange={handleChange} />
        {errors.password && <span className="error">{errors.password}</span>}
      </div>
      <button type="submit">Sign Up</button>
    </form>
  );
}

// 3. Custom hook for reusable form logic
function useForm(initialValues, validate) {
  const [values, setValues] = useState(initialValues);
  const [errors, setErrors] = useState({});
  const [submitting, setSubmitting] = useState(false);

  const handleChange = (e) => {
    const { name, value, type, checked } = e.target;
    setValues(prev => ({
      ...prev,
      [name]: type === 'checkbox' ? checked : value,
    }));
  };

  const handleSubmit = (onSubmit) => async (e) => {
    e.preventDefault();
    const validationErrors = validate(values);
    setErrors(validationErrors);
    if (Object.keys(validationErrors).length === 0) {
      setSubmitting(true);
      await onSubmit(values);
      setSubmitting(false);
    }
  };

  return { values, errors, submitting, handleChange, handleSubmit };
}

Controlled components give React full control over form state, enabling validation, conditional rendering, and submission handling without DOM manipulation.

React form implementation