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.
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>"}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 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 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.
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 minimal Higher Order Component that helps you with the 3 most annoying parts:
By colocating all of the above in one place, Formik will keep things organized--making testing, refactoring, and reasoning about your forms a breeze.
Add Formik (and optionally Yup to your project). Formik supports/recommends Yup (which is like Joi, but for the browser) for object schema validation.
npm i formik yup --save
Note: Yup is 100% optional. You are free to write your own validators.
You can also try before you buy with this demo of Formik on CodeSandbox.io
Table of Contents
Formik(options)
options
dirty: booleanerrors: { [field: string]: string }handleBlur: (e: any) => voidhandleChange: (e: React.ChangeEvent<any>) => voidhandleReset: () => voidhandleSubmit: (e: React.FormEvent<HTMLFormEvent>) => voidisSubmitting: booleanresetForm: (nextProps?: Props) => voidsetErrors: (fields: { [field: string]: string }) => voidsetFieldError: (field: string, errorMsg: string) => voidsetFieldTouched: (field: string, isTouched: boolean) => voidsetFieldValue: (field: string, value: any) => voidsetStatus: (status?: any) => voidsetSubmitting: (boolean) => voidsetTouched: (fields: { [field: string]: boolean }) => voidsetValues: (fields: { [field: string]: any }) => voidstatus?: anytouched: { [field: string]: boolean }values: { [field: string]: any }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
// onChange and an onBlur handler that you can use on every input. You also get
// handleSubmit, handleReset, errors, touched, and isSubmitting for free. This makes building custom
// inputs easy.
const EditUserForm = ({
values,
touched,
errors,
dirty,
isSubmitting,
handleChange,
handleBlur,
handleSubmit,
handleReset,
}) =>
<form onSubmit={handleSubmit}>
<label htmlFor="email">
Email
</label>
<input
id="email"
placeholder="Enter your email"
type="text"
value={values.email}
onChange={handleChange}
onBlur={handleBlur}
/>
{errors.email && touched.email && <div>{errors.email}</div>}
<input
type="text"
name="facebook"
value={values.facebook}
onChange={handleChange}
onBlur={handleBlur}
placeholder="facebook username"
/>
{errors.facebook && touched.facebook && <div>{errors.facebook}</div>}
<input
type="text"
name="twitter"
value={values.twitter}
onChange={handleChange}
onBlur={handleBlur}
placeholder="twitter username"
/>
{errors.twitter && touched.twitter && <div>{errors.twitter}</div>}
<button
type="button"
onClick={handleReset}
disabled={!dirty || isSubmitting}
>
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({
// 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.twitter,
facebook: props.user.social.facebook,
}),
// We can optionally define our a validation schema with Yup. It's like Joi, but for
// the browser. Errors from Yup will be injected as `errors` into the form.
validationSchema: Yup.object().shape({
email: Yup.string().email().required('Bruh, email is required'),
twitter: Yup.string(),
facebook: Yup.string(),
}),
// Formik lets you colocate your submission handler with your form.
// In addition to your from `values`, you have
// access to all props and some stateful helpers.
handleSubmit: (values, { props, setErrors, setSubmitting }) => {
// do stuff with your payload
// e.preventDefault(), setSubmitting, setError(undefined) are
// called before handleSubmit is. So you don't have to do repeat this.
// handleSubmit will only be executed if form values pass validation (if you specify it).
CallMyApi(props.user.id, values)
.then(
res => {
setSubmitting(false)
// do something to show success
// MyToaster.showSuccess({ message: 'Success!' })
},
err => {
setSubmitting(false)
setErrors(transformMyAPIErrorToAnObject(err))
// do something to show a rejected api submission
// MyToaster.showError({ message: 'Shit!', error: err })
}
)
},
})(EditUserForm);
Formik(options)Create a higher-order React component class that passes props and form handlers (the "FormikBag") into your component derived from supplied options.
optionsdisplayName?: stringWhen your inner form component is a stateless functional component, you can use the displayName option to give the component a proper name so you can more easily find it in React DevTools. If specified, your wrapped form will show up as Formik(displayName). If omitted, it will show up as Formik(Component). This option is not required for class components (e.g. class XXXXX extends React.Component {..}).
handleSubmit: (values: Values, formikBag: FormikBag) => voidYour form submission handler. It is passed your forms values and the "FormikBag", which includes an object containing a subset of the injected props and methods (i.e. all the methods with names that start with set<Thing> + resetForm) and any props that were passed to the the wrapped component.
props (props passed to the wrapped component)resetFormsetErrorssetFieldErrorsetFieldTouchedsetFieldValuesetStatussetSubmittingsetTouchedsetValuesNote: errors, touched, status and all event handlers are NOT included in the FormikBag.
mapPropsToValues?: (props: Props) => ValuesIf 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 inner 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.
Even if your form is not receiving any props from its parent, use mapPropsToValues to initialize your forms empty state.
validate?: (values: Values, props: Props) => FormikError<Values> | Promise<any>Note: I suggest using [validateSchema] and Yup for validation. However, validate is a dependency-free, straightforward way to validate your forms.
Validate the form's values with function. This function can either be:
errors object.// Synchronous validation
const validate = (values, props) => {
let errors = {}
if (!values.email) {
errors.email = 'Required'
} else if (!/^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i.test(values.email)) {
errors.email = 'Invalid email address'
}
//...
return errors
}
errors object// Async Validation
const sleep = ms => new Promise(resolve => setTimeout(resolve, ms))
const validate = (values, props) => {
return sleep(2000).then(() => {
let errors = {}
if (['admin', 'null', 'god']).includes(values.username) {
errors.username = 'Nice try'
}
// ...
if (Object.keys(errors).length) {
throw errors
}
})
}
validateOnBlur?: booleanDefault is true. Use this option to run validations on blur events. More specifically, when either handleBlur, setFieldTouched, or setTouched are called.
validateOnChange?: booleanDefault is false. Use this option to tell Formik to run validations on change events and change-related methods. More specifically, when either handleChange, setFieldValue, or setValues are called.
validationSchema?: SchemaA Yup schema. This is used for validation. Errors are mapped by key to the inner component's errors. Its keys should match those of values.
The following list of properties and methods will be injected into the your inner form component as React props after you "enhance"/wrap it with the Formik HoC.
props.xxxx.this.props.xxxx.Any additional props you pass to your wrapped component (including those props you do not map to form state via [mapPropsToVales]) are passed directly down untouched.
dirty: booleanReturns true if any field has been touched by any means, false otherwise. dirty is a readonly computed property and should not be mutated directly.
errors: { [field: string]: string }Form validation errors. Should match the shape of your form's values defined in Formik options. If you are using validationSchema (which you should be), keys and shape will match your schema exactly. Internally, Formik transforms raw Yup validation errors on your behalf. If you are using validate, then that function will determine the errors objects shape.
handleBlur: (e: any) => voidonBlur 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} ... />
DOM-only. Use setFieldTouched in React Native.
handleChange: (e: React.ChangeEvent<any>) => voidGeneral input change event handler. This will update the values[key] where key is the event-emitting input's name attribute. If the name attribute is not present, handleChange will look for an input's id attribute. Note: "input" here means all HTML inputs.
DOM-only. Use setFieldValue in React Native.
handleReset: () => voidReset handler. Will reset the form to its initial state. This should be passed to <button onClick={handleReset}>...</button>
handleSubmit: (e: React.FormEvent<HTMLFormEvent>) => voidSubmit handler. This should be passed to <form onSubmit={handleSubmit}>...</form>
isSubmitting: booleanSubmitting state. Either true or false. Formik will set this to true on your behalf before calling handleSubmit to reduce boilerplate.
resetForm: (nextProps?: Props) => voidImperatively 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.
setErrors: (fields: { [field: string]: string }) => voidSet errors imperatively.
setFieldError: (field: string, errorMsg: string) => voidSet the error message of a field imperatively. field should match the key of errors you wish to update. Useful for creating custom input error handlers.
setFieldTouched: (field: string, isTouched: boolean) => voidSet the touched state of a field imperatively. field should match the key of touched you wish to update. Useful for creating custom input blur handlers.
setFieldValue: (field: string, value: any) => voidSet the value of a field imperatively. field should match the key of values you wish to update. Useful for creating custom input change handlers.
setStatus: (status?: any) => voidSet a top-level status to anything you want imperatively. Useful for controlling arbitrary top-level state related to your form. For example, you can use it to pass API responses back into your component in handleSubmit.
setSubmitting: (boolean) => voidSet isSubmitting imperatively.
setTouched: (fields: { [field: string]: boolean }) => voidSet touched imperatively.
setValues: (fields: { [field: string]: any }) => voidSet values imperatively.
status?: anyA top-level status object that you can use to represent form state that can't otherwised be expressed/stored with other methods. This is useful for capturing and passing through API responses to your inner component.
status should only be modifed by calling setStatus: (status?: any) => void
touched: { [field: string]: boolean }Touched fields. Each key corresponds to a field that has been touched/visited.
values: { [field: string]: any }Your form's values. Will have the shape of the result of mapPropsToValues (if specified) or all props that are not functions passed to your wrapped component.
FormikFormik is a Higher Order Component factory; you can use it exactly like React Redux's connect or Apollo's graphql. There are 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 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 lets 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.
Sometimes you need to access React Component Lifecycle methods to manipulate your form. In this situation, you have some options:
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).
// 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="otherThing"
value={this.props.values.otherThing}
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.
Formik is 100% compatible with React Native and React Native Web. However, because of differences between ReactDOM's and React Native's handling of forms and text input, there are two differences to be aware of. This section will walk you through them and what I consider to be best practices.
Before going any further, here's a super minimal gist of how to use Formik with React Native that demonstrates the key differences:
// Formik x React Native example
import React from 'react'
import { Button, TextInput, View } from 'react-native'
import { Formik } from 'formik'
const withFormik = Formik({...})
const MyReactNativeForm = (props) => (
<View>
<TextInput
onChangeText={text => props.setFieldValue('email', text)}
value={props.values.email}
/>
<Button onPress={props.handleSubmit} title="Submit" /> //
</View>
)
export default withFormik(MyReactNativeForm)
As you can see above, the notable differences between using Formik with React DOM and React Native are:
props.handleSubmit is passed to a <Button onPress={...}/> instead of HTML <form onSubmit={...}/> component (since there is no <form/> element in React Native).<TextInput /> uses Formik's props.setFieldValue instead of props.handleChange. To understand why, see the discussion below.setFieldValue instead of handleChange?'cuz handleChange will not work in React Native...
import { Button, TextInput, View } from 'react-native'
import { Formik } from 'formik'
const withFormik = Formik({...})
// This will NOT update the TextInput when the user types
const MyReactNativeForm = (props) => (
<View>
<TextInput
name="email"
onChangeText={props.handleChange}
value={props.values.email}
/>
<Button onPress={props.handleSubmit} title="submit" />
</View>
)
export default withFormik(MyReactNativeForm)
The reason is that Formik's handleChange function expects its first argument to be synthetic DOM event where the event.target is the DOM input element and event.target.id or event.target.name matches the field to be updated. Without this, handleChange will do nothing.
In React Native, neither <TextInput />'s onChange nor onChangeText callbacks pass such an event or one like it to its callback. Instead, they do the following (emphasis added):
onChange?: function
Callback that is called when the text input's text changes.
onChangeText?: function
Callback that is called when the text input's text changes. Changed text is passed as an argument to the callback handler.
However, Formik works just fine if you use props.setFieldValue! Philisophically, just treat React Native's <TextInput/> the same way you would any other 3rd party custom input element.
In conclusion, the following WILL work in React Native:
...
// this works.
export const MyReactNativeForm = (props) => (
<View>
<TextInput
onChangeText={text => props.setFieldValue('email', text) }
value={props.values.email}
/>
<Button onPress={props.handleSubmit} />
</View>
)
...
If you are like me and do not like render callbacks, I suggest treating React Native's <TextInput/> as if it were another 3rd party custom input element:
props.setFieldValue instead of props.handleChangesetFieldValue as (in this case we'll match the React Native TextInput API and call it this.props.onChangeText for parity).// FormikReactNativeTextInput.tsx
import * as React from 'react'
import { TextInput } from 'react-native'
interface FormikReactNativeTextInputProps {
/** Current value of the input */
value: string;
/** Change handler (this will be Formik's setFieldValue ;) ) */
onChangeText: (value: string) => void;
/** The name of the Formik field to be updated upon change */
name: string;
...
// the rest of the React Native's `TextInput` props
}
export default class FormikReactNativeTextInput extends React.Component<FormikReactNativeTextInputProps, {}> {
handleChange = (value: string) => {
// remember that onChangeText will be Formik's setFieldValue
this.props.onChangeText(this.props.name, value)
}
render() {
// we want to pass through all the props except for onChangeText
const { onChangeText, ...otherProps } = this.props
return (
<TextInput
onChangeText={this.handleChange}
{...otherProps} // IRL, you should be more explicit when using TS
/>
);
}
}
Then you could just use this custom input as follows:
// MyReactNativeForm.tsx
import { View, Button } from 'react-native'
import { FormikReactNativeTextInput as TextInput } from './FormikReactNativeTextInput'
import { Formik, InjectedFormikProps } from 'formik'
interface Props {...}
interface Values {...}
export const MyReactNativeForm: React.SFC<InjectedFormikProps<Props, Values>> = (props) => (
<View>
<TextInput
name="email"
onChangeText={props.setFieldValue}
value={props.values.email}
/>
<Button onPress={props.handleSubmit} />
</View>
)
export default Formik<Props, Values>({ ... })(MyReactNativeForm)
MIT License.
FAQs
Build forms in React, without the tears
The npm package formik receives a total of 1,515,515 weekly downloads. As such, formik popularity was classified as popular.
We found that formik demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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