React Final Form is a high-performance, subscription-based form state management library for React applications. It provides a way to manage form state and validation with minimal re-renders, making it efficient for complex forms.

Pros

• Minimal re-renders due to its subscription-based model
• Lightweight and performant, especially for large forms
• Flexible API that allows for easy customization
• Supports both synchronous and asynchronous validation

Cons

• Steeper learning curve compared to simpler form libraries
• Documentation can be overwhelming for beginners
• Less opinionated, which may require more setup for common use cases
• Smaller community compared to some other popular form libraries

Code Examples

1. Basic form setup:

import { Form, Field } from 'react-final-form'

const MyForm = () => (
  <Form
    onSubmit={onSubmit}
    render={({ handleSubmit }) => (
      <form onSubmit={handleSubmit}>
        <Field name="firstName" component="input" placeholder="First Name" />
        <Field name="lastName" component="input" placeholder="Last Name" />
        <button type="submit">Submit</button>
      </form>
    )}
  />
)

2. Form with validation:

import { Form, Field } from 'react-final-form'

const validate = values => {
  const errors = {}
  if (!values.username) {
    errors.username = 'Required'
  }
  return errors
}

const MyForm = () => (
  <Form
    onSubmit={onSubmit}
    validate={validate}
    render={({ handleSubmit }) => (
      <form onSubmit={handleSubmit}>
        <Field name="username">
          {({ input, meta }) => (
            <div>
              <input {...input} placeholder="Username" />
              {meta.error && meta.touched && <span>{meta.error}</span>}
            </div>
          )}
        </Field>
        <button type="submit">Submit</button>
      </form>
    )}
  />
)

3. Form with conditional fields:

import { Form, Field } from 'react-final-form'

const MyForm = () => (
  <Form
    onSubmit={onSubmit}
    render={({ values }) => (
      <form onSubmit={handleSubmit}>
        <Field name="employmentStatus" component="select">
          <option value="employed">Employed</option>
          <option value="unemployed">Unemployed</option>
        </Field>
        {values.employmentStatus === 'employed' && (
          <Field name="employer" component="input" placeholder="Employer" />
        )}
        <button type="submit">Submit</button>
      </form>
    )}
  />
)

Getting Started

To use React Final Form in your project:

1. Install the package:

   npm install react-final-form final-form
   

2. Import and use in your React component:

   import { Form, Field } from 'react-final-form'
   
   const MyForm = () => (
     <Form
       onSubmit={onSubmit}
       render={({ handleSubmit }) => (
         <form onSubmit={handleSubmit}>
           <Field name="username" component="input" placeholder="Username" />
           <button type="submit">Submit</button>
         </form>
       )}
     />
   )
   

3. Define your onSubmit function to handle form submission.