formik

What is formik?

Formik is a popular open-source library for building forms in React and React Native. It helps with handling form state, validation, and submission. Formik provides a simple and efficient way to create controlled form components with less boilerplate code.

What are formik's main functionalities?

Form State Management

Formik simplifies form state management by providing 'initialValues' to set up the form state and 'onSubmit' to handle form submission.

{"<Formik initialValues={{ name: '' }} onSubmit={(values) => { console.log(values); }}><Form><Field name='name' type='text' /><button type='submit'>Submit</button></Form></Formik>"}

Validation and Error Handling

Formik provides a 'validate' function to define custom validation logic and uses 'ErrorMessage' to display validation errors.

{"<Formik initialValues={{ email: '' }} validate={values => { const errors = {}; if (!values.email) { errors.email = 'Required'; } else if (!/^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}$/i.test(values.email)) { errors.email = 'Invalid email address'; } return errors; }} onSubmit={(values, { setSubmitting }) => { setTimeout(() => { alert(JSON.stringify(values, null, 2)); setSubmitting(false); }, 400); }}><Form><Field name='email' type='email' /><ErrorMessage name='email' component='div' /><button type='submit'>Submit</button></Form></Formik>"}

Integration with Yup for Schema Validation

Formik can be integrated with Yup, a schema builder for value parsing and validation, to simplify form validation using a schema.

{"<Formik initialValues={{ email: '' }} validationSchema={Yup.object({ email: Yup.string().email('Invalid email address').required('Required'), })} onSubmit={(values, { setSubmitting }) => { setTimeout(() => { alert(JSON.stringify(values, null, 2)); setSubmitting(false); }, 400); }}><Form><Field name='email' type='email' /><ErrorMessage name='email' /><button type='submit'>Submit</button></Form></Formik>"}

Custom Input Components

Formik allows the use of custom input components with the 'as' prop in the 'Field' component, enabling the creation of reusable form elements.

{"<Formik initialValues={{ name: '' }} onSubmit={(values) => { console.log(values); }}><Form><Field name='name' as={MyCustomInput} /><button type='submit'>Submit</button></Form></Formik>"}

Other packages similar to formik

react-hook-form

React Hook Form is a library for managing forms in React. It uses hooks for form state management and is optimized for performance by minimizing the number of re-renders. Compared to Formik, React Hook Form is often considered faster due to its leaner API and focus on reducing re-renders.

redux-form

Redux Form leverages Redux for form state management. It integrates tightly with Redux and allows form state to be stored in the Redux store. Compared to Formik, Redux Form is more suitable for applications that already use Redux and require complex form state management across multiple components.

final-form

Final Form is a framework-agnostic form library that can be used with React via 'react-final-form'. It focuses on performance and flexibility, offering subscription-based form state management. Compared to Formik, Final Form provides more fine-grained control over form state updates and subscriptions.

README

Forms in React, without tears.

Let's face it, forms are really really verbose in React. To make matters worse, most form helpers do wayyyyy too much magic and often have a significant performace cost. Formik is minimal a Higher Order Component that helps you with the 3 most annoying parts:

1. Transforming props to a flat React state,
2. Validation and error messages
3. Transforming a flat React state back into a consumable payload for your API

Lastly, Formik helps you stay organized by colocating all of the above plus your submission handler in one place. This makes testing, refactoring, and reasoning about your forms a breeze.

Installation

Add Formik and Yup to your project. Formik uses Yup (Joi for the browser) for schema validation.

npm i formik yup --save

Table of Contents

• Usage
  • Simple Example
• API
  • Formik(options)
    • options
      • displayName: string
      • handleSubmit: (payload, FormikBag) => void)
      • mapPropsToValues?: (props) => props
      • mapValuesToPayload?: (values) => payload
      • validationSchema: Schema
    • Injected props and methods
      • error?: any
      • errors: { [field]: string }
      • handleBlur: (e: any) => void
      • handleChange: (e: React.ChangeEvent<any>) => void
      • handleChangeValue: (name: string, value: any) => void
      • handleReset: () => void
      • handleSubmit: (e: React.FormEvent<HTMLFormEvent>) => void
      • isSubmitting: boolean
      • resetForm: (nextProps?: Props) => void
      • setError(err: any) => void
      • setErrors(fields: { [field]: string }) => void
      • setSubmitting(boolean) => void
      • setTouched(fields: { [field]: string }) => void
      • setValues(fields: { [field]: any }) => void
      • touched: { [field]: string }
      • values: { [field]: any }
• Recipes
  • Ways to call Formik
  • Accessing React Component Lifecycle Functions
    • Example: Resetting a form when props change
• Authors

Usage

Simple Example

Imagine you want to build a form that lets you edit user data. However, your user API has nested objects like so.

{
   id: string,
   email: string,
   social: {
     facebook: string,
     twitter: string,
     ....
   }
}

When we are done we want our form to accept just a user prop and that's it.

// User.js
import React from 'react';
import Dialog from 'MySuperDialog';
import EditUserForm from './EditUserForm';

const EditUserDialog = ({ user }) =>
  <Dialog>
  	<EditUserForm user={user} />
  </Dialog>;

Enter Formik.

// EditUserForm.js
import React from 'react';
import Formik from 'formik';
import Yup from 'yup';

// Formik is a Higher Order Component that wraps a React Form. Mutable form values 
// are injected into a prop called `values`. Additionally, Formik injects
// an onChange handler that you can use on every input. You also get
// handleSubmit, errors, and isSubmitting for free. This makes building custom
// inputs easy.
const SimpleForm = ({ values, handleChange, handleSubmit, handleReset, errors, error, isSubmitting,  }) =>
  <form onSubmit={handleSubmit}>
    <input
      type="text"
      name="email"
      value={values.email}
      onChange={handleChange}
      placeholder="[e-mail]"
    />
    {errors.email && <div>{errors.email}</div>}
    <input
      type="text"
      name="facebook"
      value={values.facebook}
      onChange={handleChange}
      placeholder="facebook username"
    />
    {errors.facebook && <div>{errors.facebook}</div>}
    <input
      type="text"
      name="twitter"
      value={values.twitter}
      onChange={handleChange}
      placeholder="twitter username"
    />
    {errors.twitter && <div>{errors.twitter}</div>}
    {error && error.message && <div style={{color: 'red'}}>Top Level Error: {error.message}</div>}
    <button onClick={handleReset}>Reset</button>
    <button type="submit" disabled={isSubmitting}>Submit</button>
  </form>;

// Now for the fun part. We need to tell Formik how we want to validate,
// transform props/state, and submit our form.
export default Formik({
  // Give our form a name for debugging in React DevTools
  displayName: 'SimpleForm',

  // Define our form's validation schema with Yup. It's like Joi, but for
  // the browser.
  validationSchema: Yup.object().shape({
    email: Yup.string().email().required(),
    twitter: Yup.string(),
    facebook: Yup.string(),
  }),

  // We now map React props to form values. These will be injected as `values` into
  // our form. (Note: in the real world, you would destructure props, but for clarity this is
  // not shown)
  mapPropsToValues: props => ({
    email: props.user.email,
    twitter: props.user.social,
    facebook: props.user.facebook,
  }),

  // Sometimes your API needs a different object shape than your form. Formik let's 
  // you map `values` back into a `payload` before they are
  // passed to handleSubmit.
  mapValuesToPayload: values => ({
    email: values.email,
    social: { 
      twitter: values.twitter, 
      facebook: values.facebook 
    },
  }),

  // Formik lets you colocate your submission handler with your form.
  // In addition to the payload (the result of mapValuesToPayload), you have
  // access to all props and some stateful helpers.
  handleSubmit: (payload, { props, setError, setSubmitting }) => {
    // do stuff with your payload
    // e.preventDefault(), setSubmitting, setError(undefined) are // called before handleSubmit is. So you don't have to.
    // HandleSubmit will only be executed if form values pass Yup validation.
    CallMyApi(props.user.id, payload)
      .then(
        res => {
          setSubmitting(false)
          // do something to show success
          // MyToaster.showSuccess({ message: 'Success!' })
        },
        err => {
          setSubmitting(false)
          setError(err)
          // do something to show a rejected api submission
          // MyToaster.showError({ message: 'Shit!', error: err })
        }
      )
  },
})(SimpleForm);

API

Formik(options)

Create A higher-order React component class that passes props and form handlers (the "FormikBag") into your component derived from supplied options.

options

displayName: string

Set the display name of your component.

handleSubmit: (payload, FormikBag) => void)

Your form submission handler. It is passed the result of mapValuesToPayload (if specified), or the result of mapPropsToValues, or all props that are not functions (in that order of precedence) and the "FormikBag".

mapPropsToValues?: (props) => props

If this option is specified, then Formik will transfer its results into updatable form state and make these values available to the new component as props.values. If mapPropsToValues is not specified, then Formik will map all props that are not functions to the new component's props.values. That is, if you omit it, Formik will only pass props where typeof props[k] !== 'function', where k is some key.

mapValuesToPayload?: (values) => payload

If this option is specified, then Formik will run this function just before calling handleSubmit. Use it to transform the your form's values back into a shape that's consumable for other parts of your application or API. If mapValuesToPayload is not specified, then Formik will map all values directly to payload (which will be passed to handleSubmit). While this transformation can be moved into handleSubmit, consistently defining it in mapValuesToPayload separates concerns and helps you stay organized.

validationSchema: Schema

A Yup schema. This is used for validation on each onChange event. Errors are mapped by key to the WrappedComponent's props.errors. Its keys should almost always match those of WrappedComponent's props.values.

Injected props and methods

The following props and methods will be injected into the WrappedComponent (i.e. your form):

error?: any

A top-level error object, can be whatever you need.

errors: { [field]: string }

Form validation errors. Keys match the shape of the validationSchema defined in Formik options. This should therefore also map to your values object as well. Internally, Formik transforms raw Yup validation errors on your behalf.

handleBlur: (e: any) => void

onBlur event handler. Useful for when you need to track whether an input has been touched or not. This should be passed to <input onBlur={handleBlur} ... />

handleChange: (e: React.ChangeEvent<any>) => void

General input change event handler. This will update the form value according to an input's name attribute. If name is not present, handleChange will look for an input's id attribute. Note: "input" here means all HTML inputs.

handleChangeValue: (name: string, value: any) => void

Custom input change handler. Use this when you have custom inputs. name should match the key of form value you wish to update.

handleReset: () => void

Reset handler. This should be passed to <button onClick={handleReset}>...</button>

handleSubmit: (e: React.FormEvent<HTMLFormEvent>) => void

Submit handler. This should be passed to <form onSubmit={handleSubmit}>...</form>

isSubmitting: boolean

Submitting state. Either true or false. Formik will set this to true on your behalf before calling handleSubmit to reduce boilerplate.

resetForm: (nextProps?: Props) => void

Imperatively reset the form. This will clear errors and touched, set isSubmitting to false and rerun mapPropsToValues with the current WrappedComponent's props or what's passed as an argument. That latter is useful for calling resetForm within componentWillReceiveProps.

setError(err: any) => void

Set a top-level error object. This can only be done manually. It is an escape hatch.

setErrors(fields: { [field]: string }) => void

Set errors manually.

setSubmitting(boolean) => void

Set a isSubmitting manually.

setTouched(fields: { [field]: string }) => void

Set touched manually.

setValues(fields: { [field]: any }) => void

Set values manually.

touched: { [field]: string }

Touched fields. Use this to keep track of which fields have been visited. Use handleBlur to toggle on a given input. Keys work like errors and values.

values: { [field]: any }

Your form's values, the result of mapPropsToValues (if specified) or all props that are not functions passed to your WrappedComponent.

Recipes

Ways to call Formik

Formik is a Higher Order Component factory or "Monad" in functional programming lingo. In practice, you use it exactly like React Redux's connect or Apollo's graphql. There are basically three ways to call Formik on your component:

You can assign the HoC returned by Formik to a variable (i.e. withFormik) for later use.

import React from 'react';
import Formik from 'formik';

// Assign the HoC returned by Formik to a variable
const withFormik = Formik({...}); 

// Your form
const MyForm = (props) => (
 <form onSubmit={props.handleSubmit}>
   <input type="text" name="thing" value={props.values.thing} onChange={props.handleChange} />
   <input type="submit" value="Submit"/>
 </form>
);

// Use HoC by passing your form to it as an argument.
export default withFormik(MyForm);

You can also skip a step and immediately invoke (i.e. "curry") Formik instead of assigning it to a variable. This method has been popularized by React Redux. One downside is that when you read the file containing your form, its props seem to come out of nowhere.

import React from 'react';
import Formik from 'formik';

// Your form
const MyForm = (props) => (
 <form onSubmit={props.handleSubmit}>
   <input type="text" name="thing" value={props.values.thing} onChange={props.handleChange} />
   <input type="submit" value="Submit"/>
 </form>
);

// Configure and call Formik immediately
export default Formik({...})(MyForm);

Lastly, you can define your form component anonymously:

import React from 'react';
import Formik from 'formik';

// Configure and call Formik immediately
export default Formik({...})((props) => (
 <form onSubmit={props.handleSubmit}>
   <input type="text" name="thing" value={props.values.thing} onChange={props.handleChange} />
   <input type="submit" value="Submit"/>
 </form>
));

I suggest using the first method, as it makes it clear what Formik is doing. It also let's you configure Formik above your component, so when you read your form's code, you know where those props are coming from. It also makes testing much easier.

Accessing React Component Lifecycle Functions

Sometimes you need to access React Component Lifecycle methods to manipulate your form. In this situation, you have some options:

• Lift that lifecycle method up into a React class component that's child is your Formik-wrapped form and pass whatever props it needs from there
• Convert your form into a React component class (instead of a stateless functional component) and wrap that class with Formik.

There isn't a hard rule whether one is better than the other. The decision comes down to whether you want to colocate this logic with your form or not. (Note: if you need refs you'll need to convert your stateless functional form component into a React class anyway).

Example: Resetting a form when props change

// Reset form when a certain prop changes
import React from 'react';
import Formik from 'formik'

const withFormik = Formik({...});

class MyForm extends React.Component {
  componentWillReceiveProps(nextProps) {
    if (nextProps.thing !== this.props.thing) {
      this.props.resetForm(nextProps)
    }
  }

  render() {
   // Formik props are available on `this.props`
    return (
      <form onSubmit={this.props.handleSubmit}>
        <input
          type="text"
          name="thing"
          value={this.props.values.thing}
          onChange={this.props.handleChange}
        />
        <input type="submit" value="Submit" />
      </form>
    );
  }
}

export default withFormik(MyForm);

As for colocating a React lifecycle method with your form, imagine a situation where you want to use if you have a modal that's only job is to display a form based on the presence of props or not.

Authors

• Jared Palmer @jaredpalmer
• Ian White @eonwhite

MIT License.