Overview

Let's face it, forms are really verbose in React. To make matters worse, most form helpers do wayyyy too much magic and often have a significant performance cost associated with them. Formik is a small library that helps you with the 3 most annoying parts:

Getting values in and out of form state
Validation and error messages
Handling form submission

By colocating all of the above in one place, Formik will keep things organized--making testing, refactoring, and reasoning about your forms a breeze.

Motivation

I (@jaredpalmer) wrote Formik while building a large internal administrative dashboard with @eonwhite. With around ~30 unique forms, it quickly became obvious that we could benefit by standardizing not just our input components but also the way in which data flowed through our forms.

Why not Redux-Form?

By now, you might be thinking, "Why didn't you just use Redux-Form?" Good question.

According to our prophet Dan Abramov, form state is inherently ephemeral and local, so tracking it in Redux (or any kind of Flux library) is unnecessary
Redux-Form calls your entire top-level Redux reducer multiple times ON EVERY SINGLE KEYSTROKE. This is fine for small apps, but as your Redux app grows, input latency will continue to increase if you use Redux-Form.
Redux-Form is 22.5 kB minified gzipped (Formik is 12.7 kB)

My goal with Formik was to create a scalable, performant, form helper with a minimal API that does the really really annoying stuff, and leaves the rest up to you.

My talk at React Alicante goes much deeper into Formik's motivation and philosophy, introduces the library (by watching me build a mini version of it), and demos how to build a non-trivial form (with arrays, custom inputs, etc.) using the real thing.

Influences

Formik started by expanding on this little higher order component by Brent Jackson, some naming conventions from Redux-Form, and (most recently) the render props approach popularized by React-Motion and React-Router 4. Whether you have used any of the above or not, Formik only takes a few minutes to get started with.

Installation

You can install Formik with NPM, Yarn, or a good ol' <script> via unpkg.com.

NPM

 npm install formik --save

 yarn add formik

Formik is compatible with React v15+ and works with ReactDOM and React Native.

You can also try before you buy with this demo of Formik on CodeSandbox.io

In-browser Playgrounds

You can play with Formik in your web browser with these live online playgrounds.

The Gist

Formik keeps track of your form's state and then exposes it plus a few reusable methods and event handlers (handleChange, handleBlur, and handleSubmit) to your form via props. handleChange and handleBlur work exactly as expected--they use a name or id attribute to figure out which field to update.

1 import React from 'react';
2 import { Formik } from 'formik';
3 
4 const Basic = () => (
5   <div>
6     <h1>Anywhere in your app!</h1>
7     <Formik
8       initialValues={{ email: '', password: '' }}
9       validate={values => {
10         const errors = {};
11         if (!values.email) {
12           errors.email = 'Required';
13         } else if (
14           !/^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}$/i.test(values.email)
15         ) {
16           errors.email = 'Invalid email address';
17         }
18         return errors;
19       }}
20       onSubmit={(values, { setSubmitting }) => {
21         setTimeout(() => {
22           alert(JSON.stringify(values, null, 2));
23           setSubmitting(false);
24         }, 400);
25       }}
26     >
27       {({
28         values,
29         errors,
30         touched,
31         handleChange,
32         handleBlur,
33         handleSubmit,
34         isSubmitting,
35         /* and other goodies */
36       }) => (
37         <form onSubmit={handleSubmit}>
38           <input
39             type="email"
40             name="email"
41             onChange={handleChange}
42             onBlur={handleBlur}
43             value={values.email}
44           />
45           {errors.email && touched.email && errors.email}
46           <input
47             type="password"
48             name="password"
49             onChange={handleChange}
50             onBlur={handleBlur}
51             value={values.password}
52           />
53           {errors.password && touched.password && errors.password}
54           <button type="submit" disabled={isSubmitting}>
55             Submit
56           </button>
57         </form>
58       )}
59     </Formik>
60   </div>
61 );
62 
63 export default Basic;

Reducing boilerplate

The code above is very explicit about exactly what Formik is doing. onChange -> handleChange, onBlur -> handleBlur, and so on. However, to save you time, Formik comes with a few extra components to make life easier and less verbose: <Form />, <Field />, and <ErrorMessage />. They use React context to hook into the parent <Formik /> state/methods.

1 // Render Prop
2 import React from 'react';
3 import { Formik, Form, Field, ErrorMessage } from 'formik';
4 
5 const Basic = () => (
6   <div>
7     <h1>Any place in your app!</h1>
8     <Formik
9       initialValues={{ email: '', password: '' }}
10       validate={values => {
11         const errors = {};
12         if (!values.email) {
13           errors.email = 'Required';
14         } else if (
15           !/^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}$/i.test(values.email)
16         ) {
17           errors.email = 'Invalid email address';
18         }
19         return errors;
20       }}
21       onSubmit={(values, { setSubmitting }) => {
22         setTimeout(() => {
23           alert(JSON.stringify(values, null, 2));
24           setSubmitting(false);
25         }, 400);
26       }}
27     >
28       {({ isSubmitting }) => (
29         <Form>
30           <Field type="email" name="email" />
31           <ErrorMessage name="email" component="div" />
32           <Field type="password" name="password" />
33           <ErrorMessage name="password" component="div" />
34           <button type="submit" disabled={isSubmitting}>
35             Submit
36           </button>
37         </Form>
38       )}
39     </Formik>
40   </div>
41 );
42 
43 export default Basic;

Read below for more information...

Complementary Packages

As you can see above, validation is left up to you. Feel free to write your own validators or use a 3rd party library. Personally, I use Yup for object schema validation. It has an API that's pretty similar to Joi / React PropTypes but is small enough for the browser and fast enough for runtime usage. Because I ❤️ Yup sooo much, Formik has a special config option / prop for Yup called validationSchema which will automatically transform Yup's validation errors into a pretty object whose keys match values and touched. Anyways, you can install Yup from npm...