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Simple validations for node and the browser.


A DOM-independent validation library for Node.js, io.js and the browser.

It supports both sync

It allows you to seamlessly validate full javascript objects, defining custom messages, labels, and validations, with full support for asynchronous validations with promises. It supports conditional validations, and has powerful, consistent error structuring and utility methods for manipulating your errors' output any way you can imagine.

var mainRules = Checkit(rules);
  .then(function(validatedFields) {
    console.log('The fields: ' + _.keys(validatedFields).join('') + ' were validated!');
  .caught(Checkit.Error, function(err) {
    $("#errors").html(, key) {
      return '<li>' + key + '' + val.first().message + '</li>';


npm install checkit


The easiest way to use the library is with webpack or browserify


Checkit(validators, [options])

The main Checkit constructor may be called with or without the new keyword, taking a hash of fields/rules for these fields to be validated.



Used to specify the default language key for using a particular language file, currently en, es, ru and fr are supported.


Specifies labels for use in error messages for specific keys


Adds specific messages for individual errors


checkit.validate (alias)

var checkit = new Checkit({
  firstName: 'required',
  lastName: 'required',
  email: ['required', 'email']
var body = {
  email: '',
  firstName: 'Tim',
  lastName: 'Griesser',
  githubUsername: 'tgriesser'
}; {
}).catch(Checkit.Error, function(err) {


checkit.validateSync (alias)

var checkit = new Checkit({
  firstName: 'required',
  lastName: 'required',
  email: ['required', 'email']
var body = {
  email: '',
  firstName: 'Tim',
  lastName: 'Griesser',
  githubUsername: 'tgriesser'
var [err, validated] = checkit.validateSync(body)
// ... 

Checkit.check(key, value, rules)

Checkit.check('email', email, ['required', 'validEmail'])
  .catch(function(err) {

Checkit.checkSync(key, value, rules)

// ES6... 
var [err, resp] = Checkit.checkSync('email', email, ['required', 'validEmail'])  
if (err) {
} else {
  // ... 

Available Validators

Validation Name Description
accepted The value must be yes, on, or 1. This is useful for validating "Terms of Service" acceptance.
alpha The value must be entirely alphabetic characters.
alphaDash The value may have alpha-numeric characters, as well as dashes and underscores.
alphaNumeric The value must be entirely alpha-numeric characters.
alphaUnderscore The value must be entirely alpha-numeric, with underscores but not dashes.
arguments The value must be a javascript "arguments" object.
array The value must be a valid array object.
base64 The value must be a base64 encoded value.
between:min:max The value must have a size between the given min and max.
boolean The value must be a javascript boolean.
contains:value The value must contain the value. For a string, it does an "indexOf" check, an array "_.indexOf" and for an object "_.has".
date The value must be a valid date object.
different:fieldName The given field must be different than the `fieldName` under validation.
email The field must be a valid formatted e-mail address.
empty The value under validation must be empty; either an empty string, an empty, array, empty object, or a falsy value.
exactLength:value The field must have the exact length of "val".
exists The value under validation must not be undefined.
finite The value under validation must be a finite number.
function The value under validation must be a function.
greaterThan:value The value under validation must be "greater than" the given value.
greaterThanEqualTo:value The value under validation must be "greater than" or "equal to" the given value.
integer The value must have an integer value.
ipv4 The value must be formatted as an IPv4 address.
ipv6 The value must be formatted as an IPv6 address.
lessThan:value The value must be "less than" the specified value.
lessThanEqualTo:value The value must be "less than" or "equal to" the specified value.
luhn The given value must pass a basic luhn (credit card) check regular expression.
matchesField:fieldName The value must exactly match the value of another `fieldName` under validation.
max:value The value must be less than a maximum value. Strings, numerics, and files are evaluated in the same fashion as the size rule.
maxLength:value The value must have a length property which is less than or equal to the specified value. Note, this may be used with both arrays and strings.
min:value The value must have a minimum value. Strings, numerics, and files are evaluated in the same fashion as the size rule.
minLength:value The value must have a length property which is greater than or equal to the specified value. Note, this may be used with both arrays and strings.
NaN The value must be NaN.
natural The value must be a natural number (a number greater than or equal to 0).
naturalNonZero The value must be a natural number, greater than or equal to 1.
null The value must be null.
number The value must be a javascript Number.
numeric The value must have a numeric value.
object The value must pass an _.isObject check.
plainObject The value must be an object literal.
regExp The value must be a javascript RegExp object.
required The value must be present in the input data.
string The value must be a string type.
url The value must be formatted as an URL.
uuid Passes for a validly formatted UUID.

Conditional Validations

Sometimes you may wish to require a given field conditionally, for example require a field only if another field has a greater value than 100. Or you may need two fields to have a given value only when another field is present. Adding these validation rules doens't have to be a pain. First, create a Checkit instance with the main rules that never change:

var checkit = new Checkit({
  firstName: ['required'],
  lastName: ['required'],
  email: ['required', 'email']

Then use the maybe method to add additional rules:

.maybe(rules, handler)

The first of the maybe method is the hash of validation fields / settings, similar to the main Checkit object. The second argument is a function, evaluated with the object being validated, and if it returns explicitly true or with a promise fulfilling with true, it will add an additional validator to the Checkit object.

This method makes building complex conditional validations a snap.

// In this example, the "authorBio" field is only required if there are 
// more than 5 books specified in the input object 
checkit.maybe({authorBio: ['required', 'max:500']}, function(input) {
  return input.books > 5;

Advanced & Custom Validators:

First, and simplest, you can specify a function on the validation array for a property. For example:

  email: ['email', function(val) {
    return knex('accounts').where('email', '=', val).then(function(resp) {
      if (resp.length > 0) throw new Error('The email address is already in use.')

You may also specify an object in one of the validator slots, specifying at the minimum a rule, and optionally params, label, and message.

  email: {
    rule: 'email',
    label: 'Email'
  first_name: [{
    rule: 'required',
    message: 'You must supply a first name value!!'
  }, {
    rule: 'minLength:3',
    label: 'first name of this application'
  arr: {
    rule: 'contains',
    params: [10] // Number => Different behavior than "contains:10" 

You may also use the context parameter passed to run when using a function on the validation array of a property. This can be particularly useful if your validation function needs to execute within a transaction:

  email: {
    rule: function(val, params, context){
      var query = knex('users');
      if (context && context.transacting){
      return query.where('email', '=', val)
        .andWhere('id', '<>',
          if (resp.length > 0){
            throw new Error('The email address is already in use.');

Second, you may add a custom validator to the Checkit.Validator object's prototype, returning a boolean value or a promise.

Checkit.Validator.prototype.unused = function(val, table, column) {
  return knex(table).where(column, '=', val).andWhere('id', '<>', {
    if (resp.length > 0) {
      throw new Error('The ' + table + '.' + column + ' field is already in use.');
  email: ['email', 'unused:accounts:email']

Checkit Errors

One of the main features of Checkit is the error handling; By extending the error object with utility methods from underscore, the errors are even easier to work with.


The main Error object, Checkit.Error is returned from the has several helper methods & properties, as well as a number of utility methods:


The "errors" property of a Checkit.Error object is a hash of errors for each of the fields which are considered "invalid" in any way by the validation rules. The keys in this hash are the invalid fields, and the values are Checkit.FieldError objects, which in-turn have an errors attribute, an array containing errors for each failed rule.


The get method returns the Checkit.FieldError object for a specific key, or undefined if one does not exist.


Useful for debugging, the toString method converts the Checkit error into a human readable representation of the failed validation. If the flat argument is passed as a "truthy" value, it will output only the first ValidationError in the FieldError; otherwise it will output each validation message in a comma separated string.


Converts the current error object to a json representation of the error, for easy use/refinement elsewhere. For other methods, such as map, reduce, each, see the utility methods section.


A FieldError is an error that contains all of the sub-errors for the validation of an individual item in the validated hash.


The errors property of a FieldError is


A ValidationError is the result of an individual error in the field rule.

Error Utility Methods

The following methods are underscore methods proxied to the Checkit.Error and Checkit.FieldError objects, for easy manipulation of the .errors object contained in each.

shared (Checkit.Error & FieldError)
Checkit.Error only
Checkit.FieldError only

Other Helpers


The Checkit.labelTransform method takes a function that receives the field name and returns a human-readable label for use in error messages.

Change Log


  • Expect a global Promise instance. Breaking change #69
  • Add meaningful message for integer validation. #46
  • Add string validation. #58
  • Compatible with Lodash 4.x only. #55
  • More permissive email regex. #61, #68
  • Only bundle required lodash methods. #69


  • Separate codepath for server (bluebird) and client (when.js)
  • Add French and Russian translations.
  • Allow new longer top level domains in emails.


  • Minor bugfixes


  • Major internal refactoring, using when.js to shave bytes in the browser build.
  • Added sync api with runSync / checkSync / validateSync
  • Alias validate for run


  • CheckIt is now renamed Checkit
  • Flipped the validations and target arguments, so the syntax is now Checkit(validations).run(input) rather than Checkit(input).run(validations), allowing for re-use of the validation objects.
  • Tons of other internal changes, probably too many to list, pretty much a rewrite from 0.1.0


Initial release