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:
- Transforming props to a flat React state
- Validation and error messages
- 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.
Add Formik and Yup to your project. Formik uses Yup (which is like Joi, but for the browser) for object schema validation.
npm i formik yup --saveYou can also try before you buy with this demo on CodeSandbox.io
- Basic
- Building your own input primitives
- Working with 3rd party input components
- Accessing React lifecycle functions
Table of Contents
- Usage
- API
Formik(options)options- Injected props and methods
error?: anyerrors: { [field: string]: string }handleBlur: (e: any) => voidhandleChange: (e: React.ChangeEvent<any>) => voidhandleChangeValue: (name: string, value: any) => voidhandleReset: () => voidhandleSubmit: (e: React.FormEvent<HTMLFormEvent>) => voidisSubmitting: booleanresetForm: (nextProps?: Props) => voidsetError(err: any) => voidsetErrors(fields: { [field: string]: string }) => voidsetSubmitting(boolean) => voidsetTouched(fields: { [field: string]: boolean }) => voidsetValues(fields: { [field: string]: any }) => voidtouched: { [field: string]: boolean}values: { [field: string]: any }
- Recipes
- Authors
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,
touched,
errors,
error,
handleChange,
handleSubmit,
handleBlur,
handleReset,
isSubmitting
}) =>
<form onSubmit={handleSubmit}>
<input
type="text"
name="email"
value={values.email}
onChange={handleChange}
onBlur={handleBlur}
placeholder="john@apple.com"
/>
{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>}
{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({
// 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.twitter,
facebook: props.user.social.facebook,
}),
// Sometimes your API needs a different object shape than your form. Formik lets
// 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 do repeat this.
// 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);Create a higher-order React component class that passes props and form handlers (the "FormikBag") into your component derived from supplied options.
When 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 {..}).
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".
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.
If this option is specified, then Formik will run this function just before calling handleSubmit. Use it to transform 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.
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.
The following props and methods will be injected into the WrappedComponent (i.e. your form):
A top-level error object, can be whatever you need.
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.
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} ... />
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.
Custom input change handler. Use this when you have custom inputs. name should match the key of form value you wish to update.
Reset handler. This should be passed to <button onClick={handleReset}>...</button>
Submit handler. This should be passed to <form onSubmit={handleSubmit}>...</form>
Submitting state. Either true or false. Formik will set this to true on your behalf before calling handleSubmit to reduce boilerplate.
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.
Set a top-level error object. This can only be done manually. It is an escape hatch.
Set errors manually.
Set isSubmitting manually.
Set touched manually.
Set values manually.
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.
Your form's values, the result of mapPropsToValues (if specified) or all props that are not functions passed to your WrappedComponent.
Formik 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:
- 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).
// 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.handleChangeValue('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:
- Formik's
props.handleSubmitis passed to a<Button onPress={...}/>instead of HTML<form onSubmit={...}/>component (since there is no<form/>element in React Native). <TextInput />uses Formik'sprops.handleChangeValueinstead ofprops.handleChange. To understand why, see the discussion below.
'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 props.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, props.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.handleChangeValue! 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.handleChangeValue('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:
- Write your own class wrapper around the custom input element
- Pass the custom component
props.handleChangeValueinstead ofprops.handleChange - Use a custom change handler callback that calls whatever you passed-in
handleChangeValueas (in this case we'll match the React Native TextInput API and call itthis.props.onChangeTextfor 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 handleChangeValue ;) ) */
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 handleChangeValue
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 } from 'react-native'
import Button from './MyButton' // Assume this just exists
import { FormikReactNativeTextInput as TextInput } from './FormikReactNativeTextInput'
import { Formik, InjectedFormikProps } from 'formik'
interface Props {...}
interface Values {...}
interface Payload {...}
export const MyReactNativeForm: React.SFC<InjectedFormikProps<Props, Values>> = (props) => (
<View>
<TextInput
name="email"
onChangeText={props.handleChangeValue}
value={props.values.email}
/>
<Button onPress={props.handleSubmit} />
</View>
)
export default Formik<Props, Values, Payload>({ ... })(MyReactNativeForm)- Jared Palmer @jaredpalmer
- Ian White @eonwhite
MIT License.