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Red hot form validation for React šŸŒ¶
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Red hot validation for React šŸŒ¶

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yarn add calidation

What's this?

This is a validation library for React! It provides you with powerful and flexible validation, which is probably what you're looking for.

I have written the best blog post of all time about this.

How do you even?

Let's say you have a form you want to validate. Remove that old school <form /> tag and replace it with a fly af <FormValidation /> component!

Step 1: Specify your fields

First, you specify a config object that specifies the names of the fields you want to validate, and the validators to apply to each field.

const formConfig = {
    username: {
        isRequired: 'Username is required!',
    password: {
        isRequired: 'Password is also required!',
        isMinLength: {
            message: 'Password must at least be 8 characters long',
            length: 8,

In this config, we validate two fields - username and password. These keys are matched with your <input name /> property. Each matching object is a list of validators.

Here, the key is the name of the validator, and the value is either the error message as a string, or an object with a simple validation configuration. You can add as many validators as you want, and they'll be run from top to bottom. For more about validators, go to the validators section!

Validate that form

Alright, so this is how it looks:

import { FormValidation } from 'calidation';

const config = {...}; // See above
const MyForm = props => (
    <FormValidation onSubmit={props.onSubmit} config={config}>
        {({ errors, fields, submitted }) => (
                    Username: <input name="username" value={fields.username} />
                    {submitted && errors.username && <span>{errors.username}</span>}
                    Password: <input name="password" value={fields.password} />
                    {submitted && errors.password && <span>{errors.password}</span>}
                <button>Log in</button>

The <FormValidation /> component accepts a function as a child, which is called with an options object containing field values, errors and so on.

The <FormValidation /> component renders a <form /> tag, so you get a nicer user experience out of the box! You can pass an onSubmit event handler, which will be called with the field values and errors:

onSubmit = ({ fields, isValid }) => {
    if (isValid) {

Validate complex forms

Some times, you end up with advanced forms, and you don't want to specify all the fields in the same configuration object. There might be many reasons for this, like when certain parts of your form is visible only if certain conditions are met.

For those cases, we have two new components - <Form /> and <Validation />.

The <Form /> component works as the <form /> HTML tag, wrapping the entire complex form. You can put this at the top level of your page container component, for example. This component accepts an onSubmit handler, similar to what you're used to from <FormValidation />.

The <Validation /> component is a descendant of a given <Form /> component, and wraps your input fields, dropdowns and radio buttons. It expects a config prop, an optional initialFields prop, and a function as a child, just like <FormValidation />. Here

Here's an example:

import { Form, Validation } from 'calidation';
const MyPage = props => (
    <Form onSubmit={props.onSubmit}>
        <Validation config={props.config}>
            {({ fields }) => (
                    Who is your daddy?
                    <input name="daddy" value={fields.daddy} />
        {/* ...tons of other components and other stuff */}
        <Validation config={props.anotherConfig}>
            {({ fields }) => (
                    What does he do?
                    <input name="dadWork" value={fields.dadWork} />

The onSubmit handler will receive a merged object of all the validated fields below it, as well as a merged object of all the errors:

const onSubmit = ({ fields, errors, isValid }) => {
    // fields and errors now contain both `daddy` and `dadWork`
    // isValid is true if all forms are valid, otherwise false.


All validators require a configuration object that looks like this:

someField: {
    isRequired: {
        message: 'This is the error message shown if the validation fails',

If you only specify the message key, you can just pass the message string directly, like this:

someField: {
    isRequired: 'This is the error message shown if the validation fails',

You can skip validation of a certain validator if you specify a validateIf function. It will receive the other validated fields as an argument.

someField: {
    isRequired: {
        message: 'You need to answer this question',
        validateIf: ({ fields }) => fields.someOtherField === 'foo',

If you only want to display errors when the field has been edited, you can use the isDirty flag.

someField: {
    isMinLength: {
        length: 5,
        message: 'Must be minimum of 5 characters',
        validateIf: ({ isDirty }) => isDirty,

If you want to do cross validation, or just need access to the other field inputs and / or errors, each validator also accepts a function that receives all fields and the current error state.

password: {
    isRequired: 'You need a password',
repeatPassword: {
    isRequired: 'Please fill out the password a second time',
    isEqual: ({ fields }) => ({
        message: 'The two password must match',
        value: fields.password,
        validateIf: fields.password.length > 0, // this can be a boolean too!

Finally, please note that validation happens from top to bottom. The validation will quit once it encounters an error, so you can have multiple levels of validators if you so please.

Default validators

calidation comes with a lot of validators built in. These should be enough for most common use-cases. You'll find them all in the sister package calidators.


Validates that a field has some content.

someField: {
    isRequired: 'This field is required', // shorthand
    isRequired: { message: 'This field is required' },


Validates that a field only contains numeric characters

someField: {
    isNumber: 'You need to enter a number', // shorthand
    isNumber: { message: 'You need to enter a number' },


Validates that a field equals a given value. The value is cast to a String, and then checked for equality with the === operator.

someField: {
    isEqual: {
        message: 'You need to enter "yes"',
        value: 'yes',

isGreaterThan / isLessThan

Validates that a field is greater or less than a given number.

someField: {
    isGreaterThan: {
        message: 'You need to be at least 18 years old',
        value: 17,
    isLessThan: {
        message: 'You can\'t be older than 70 years old',
        value: 66,


Validates that a field is a potentially valid email address.

someField: {
    isEmail: 'Please enter a valid e-mail address', // Shorthand
    isEmail: { message: 'Please enter a valid e-mail address' },


Validates that a field matches a given regular expression.

someField: {
    isRegexMatch: {
        message: 'You need to enter four digits',
        regex: /^\d{4}$/,


Validates that a field is present in a provided whitelist. The whitelist must be an array.

firstName: {
    isWhitelisted : {
        message: 'Bros only, bro',
        whitelist: ['Chad', 'Bret'],


Validates that a field is not present in a provided blacklist. The blacklist must be an array.

firstName: {
    isBlacklisted : {
        message: 'Bros are not welcome',
        blacklist: ['Chad', 'Bret'],


Validates that a field is at least a given number of characters long.

someField: {
    isMinLength: {
        message: 'You need at least four characters',
        length: 4,


Validates that a field is at most a given number of characters long.

someField: {
    isMaxLength: {
        message: 'You can at most have four characters',
        length: 4,


Validates that a field is exactly a given number of characters long.

someField: {
    isExactLength: {
        message: 'Norwegian postal codes are four digits long',
        length: 4,

Custom validators

You can add your own too! In that case, wrap your app with the <ValidatorsProvider /> component, and pass it an object with your custom validators. It can look like this:

import { ValidatorsProvider } from 'calidation';
const extraValidators = {
    isEven: (config, { errors, fields, isDirty }) => value =>
        Number(value) % 2 !== 0 ? config.message : null,
    isOdd: (config, { errors, fields, isDirty }) => value =>
        Number(value) % 2 !== 1 ? config.message : null,

<ValidatorsProvider validators={extraValidators}>
    <App />

See how I implemented those custom validators? It's a curried function that first receives a config object, then the value, and then returns either an error message or null. You might want to let them accept the empty string too, in case your field is not required.



import { FormValidation } from 'calidators';

When you have a simple form to validate.


Accepts all of the props from Form and Validation below.


The FormContext object represents the core internal state of the form and is passed through event callbacks and into template functions.

    dirty: object, // Object with all fields isDirty state, keyed per field
    errors: object, // Object with all error messages, keyed per field
    fields: object, // Object with all field inputs, keyed per field
    isValid: bool, // Boolean indicating whether your form is valid or not
    resetAll: func, // call this to programmatically trigger a full state reset
    setError: func, // callback accepting a diff object, updating errors like setState
    setField: func, // callback accepting a diff object, updating fields like setState
    submit: func, // call this to programmatically trigger a submitted state
    submitted: bool, // flag showing whether the form has been submitted once or not


import { Form } from 'calidators';

When you want to wrap a complex form (in conjunction)


onChange: func

This callback is fired whenever a form change event is triggered. This could happen on any input in the form, not necessarily associated with a validated input. This callback is also called before any state changes have been made.

The onChange function is called with the original change event as its only prop.

onReset: func

This callback is fired whenever the form is reset. That can happen whenever somebody clicks a button with type "reset", or calls the resetAll function passed in the children function.

The onReset function is called with no parameters.

onSubmit: func

This callback is fired whenever the form is submitted. That can happen whenever somebody clicks the submit button, hits enter in the form, or calls the submit function passed in the children function.

The onSubmit function is called with the FormContext object as its only prop.

onUpdate: func

This callback is fired whenever the form state changes. This can happen when Validation components are registered or unregistered, when a field is updated by the user or when the setField method is called, when the setError method is called, or when the form is reset or the resetAll method is called.

The onUpdate function is called with the FormContext object as its only prop.


import { Validation } from 'calidators';

When you want to wrap a sub-set of your form in validation logic (in conjunction with the Form tag)


children: func.isRequired

The children function is called with the FormContext object as its only prop.

config: object.isRequired

The config object specifies what you want to validate, and which validators to apply to it.

Each validator can accept an object with a message key or - in the case where you don't have to specify anything other than a validation message - just a string with the error message.

initialValues: object

The initialValues object lets you specify the initial values of the form fields. These values are available from the fields argument in the children function, which lets you control your form fields.

transforms: object

The transforms object lets you apply transforms to the value before it is stored and validated against. Each key should map to a field name and be a function that receives and returns a value. This is useful if you wish to convert a value's type or enforce casing.

    foo: (value) => parseInt(value),
    bar: (value) => !!value ? 'YES' : 'NO',
    etc: (value) => value.toLowerCase(),


import { ValidatorsProvider } from 'calidators';

When you want to provide your application with a few more validators. Wrap your app with this at the top level.


validators: object

An object with functions according to the validators spec. TL;DR: A function that returns a function that returns a function that decides whether or not your input if fair. Relax - here's an example:

const validators = {
    isBadTaste = (config, context) => value => value === 'Justin Bieber',

<ValidatorsProvider validators={validators}>

The context is an object with the following props:

    errors: object, // object with the same keys as `fields`, but with error messages
    fields: object, // object with the form field values, to make controlled components
    isDirty: bool, // flag showing whether the current field has been modified

Want to contribute?

I'd love some help! Report bugs, help me document stuff, create new validators and add new features!

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