Simple and highly extensible validation library
Last updated 5 years ago by wilkerlucio .
MIT · Repository · Bugs · Original npm · Tarball · package.json
$ cnpm install composed-validations 
SYNC missed versions from official npm registry.


Build Status

Javascript validation library that makes sense.



Before we see any code, I would first like to explain the basis of composed-validations.

The entire framework works around a really simple interface, remember that, it is:


All of the validators responds to this interface, and each validator is a single small piece that just validates a single value. In order to validate complex values, you use compositional validators that will compose your complex validation. We will learn more about that though this documentation.


Currently we ship the library in two formats, you can use the NPM version:

npm install -S composed-validations

Or you can download the browser version (it's about 5kb when minified+gzip).

Basic validations

Let's start with the simplest validations that just checks if a value is present:

var cv = require('composed-validations');

var validator = cv.presence()

validator.test(null); // will raise a ValidationError, since null is not a present value
validator.test('ok'); // will just not raise any errors, since it's valid

And let's look at one more, just for the sake of exemplify:

var cv = require('composed-validations');

var validator = cv.range(10, 20)

validator.test(9); // will raise a ValidationError, since null is out of range
validator.test(10); // will just not raise any errors, since it's valid
validator.test(15); // will just not raise any errors, since it's valid
validator.test(25); // will raise a ValidationError, since null is out of range

So, each validator should be constructed and configured, and them it will just respond to the test when it's called.

The examples above are really simple ones, so, let's get into the composed validators on the next section.

Async Validations

The async validations works pretty much the same way as sync validations, the only difference is that instead of throwing the error right away, it will must return a Promise, that can resolve (we don't care on what) or get rejected (when the validation fails).

Right now we don't provide any async validators out of the box because I couldn't find any general ones that worth to be built-in. But it's pretty easy to implement your own, check the Creating asynchronous validators section for more info on that.

The point here is just to have you know about validators may return a Promise instead of raising the error right away.

We don't provide async validators, but we provide some mechanims for you to use them, we will talk more about that later on this doc.

If you are not familiar with the Promise concept, this is a good place to start:

Composing Validations

Ok, now that you got the basics, let's go a step further, we are going to get into object fields validations, but before that, let's first understand what "complex multi-field validations" are about; what happens when you do a complex validation is actually just having many validations that runs togheter. And for multi validations running togheter, let's introduce the MultiValidator:

var cv = require('composed-validations');

var validator = cv.multi()
  .add(cv.include(['optionA', 'optionB']);

validator.test(null); // will raise an error that has information from both failures

The example above is silly because the IncludeValidator would reject the null anyway, but I hope you understand the point being made, that is, you can have multiple validations happening togheter into a given value. So, what about objects? Objects are just values as strings, lists or any other... We just need a way to target specific parts of the object, and for that we have the FieldValidator:

var cv = require('composed-validations');

// let's create a PresenceValidator, that is wrapped by a FieldValidator
var validator = cv.field('name', cv.presence());

validator.test(null); // will raise an error because it cannot access fields on falsy values
validator.test({age: 15}); // will raise an error because the field 'name' is not present on the object
validator.test({name: null}); // this time it will fail because the PresenceValidator will not allow the null
validator.test({name: "Mr White"}); // you think it will pass? "You are god damn right!"

So, know we know 2 things:

  1. We can run multiple validations togheter
  2. We can use FieldValidator to validates specific fields on the object

Do the math, and you will realise you can validate complex objects as:

var cv = require('composed-validations');

var validator = cv.multi()
  .add(cv.field('name', cv.presence())
  .add(cv.field('email', cv.presence());

validator.test({name: "cgp", email: ""});

Nice hum? Both you are probably thinking "oh boy it's verbose"... And we agree, also, this generic way of handling fields is great in terms of extensibility, but is not very friendly when you trying to get information about problems on specific fields, or if you want to run tests on a single field instead of running them all. And that's why the MultiValidator is just the beginning, there are other more specific "multi-validation" classes to help you out. For now let's take a look at the one you probably gonna use the most, the StructValidator:

var cv = require('composed-validations');

var addressValidator = cv.struct()
  .validate('street', cv.presence())
  .validate('zip', cv.format(/\d{5}/) // silly zip format
  .validate('city', cv.presence())
  .validate('state', cv.presence());

  street: 'street name',
  zip: '51235',
  city: 'Tustin',
  state: 'CA'
}); // test all!

addressValidator.testField('street'); // this will run only the tests that targets the 'street' field

The StructValidator is just an extension of MultiValidator you can still use the regular add method, it's just that StructValidator wraps a lot of knowledge about struct type data, so it will do the hard work so you don't have to.

And going further to make sure you understand the power of composing validations, check this out:

var cv = require('composed-validations');

// let's say this will import the validator from the previous example
addressValidator = require('./address_validator');

userValidator = cv.struct();
  .validate('name', cv.presence())
  .validate('age', cv.range(0, 200))
  .validate('userType', cv.include(['member', 'admin']))
  // in fact, the address validator is just another composed validator, so just send it!
  .validate('address', addressValidator);

  name: 'The Guy',
  age: 26,
  userType: 'admin',
  address: {
    street: 'street name',
    zip: '51235',
    city: 'Tustin',
    state: 'CA'
}); // and there you have it, all validations will go into the right places!

And that's what composed validations is about, there still a lot that wasn't covered here, things like mixing sync and async validations into multi validators, making fields optional, replacing error messages... Oh boy that's still a lot that you can know about this library, check each validator specific documentation for details on each feature for more details.

Creating custom validators

Creating synchronous validators

Being able to add custom validators is something that I really care about, the framework was designed and built upon a simple interface in order to make as easy as possible to create new validators and use it togheter with others.

Remember the interface that we talked about on the introduction?


I mean it, so, let's implement a simple validator that validates if a value is equal to a specific value. And let's do it into the simplest possible way:

var cv = require('custom-validations');

var equalToHelloValidator = {
  test: function(value) {
    if (value != 'hello') {
      throw cv.error('is not equal to hello', value, this);

    // you must return the same input as given to you, unless you are writing a
    // specifically to transform the data
    return value;

// using the validator
equalToValidator.test('not'); // faill
equalToValidator.test('hello'); // ok

As you see, the only thing that we need from custom-validations is the ValidationError, the reason why you must use it to fire errors instead of a regular error, is because that way we can differentiate validation errors from other kinds of errors (that would be handle in different ways). The signature for instantiating a new ValidationError is:

cv.error(message, value, validator);

This information helps other validators and errors handlers to deal better with error information.

After you have it, just another quick example on how to use it with the regular validators:

var cv = require('custom-validations');

var equalToHelloValidator = {
  test: function(value) {
    if (value != 'hello') {
      throw cv.error('is not equal to hello', value, this);

var modelValidator = cv.struct()
  .validate('someField', equalToHelloValidator);

modelValidator.test({someField: 'hello'}); // ok

You usually want a bit of more flexibility, but that's easy to accomplish, instead of making our validator as a crude object, we can use a factory to generate it in a more customizable way, as so:

var cv = require('composed-validations');

var equalToValidator = function (given) {
  return {
    test: function(value) {
      if (value != given) {
        throw cv.error("is not equal to " + JSON.stringify(given), value, this);

var modelValidator = cv.struct()
  .validate('someField', equalToValidator('hello'));

modelValidator.test({someField: 'hello'}); // ok

I love the power of closures, don't you?

You can use class style if you prefer:

var cv = require('composed-validations');

var EqualToValidator = function (given) {
  this.given = given;

EqualToValidator.prototype.test = function(value) {
  if (value != this.given) {
    throw cv.error("is not equal to " + JSON.stringify(this.given), value, this);

var modelValidator = cv.struct()
  .validate('someField', new EqualToValidator('hello'));

modelValidator.test({someField: 'hello'}); // ok

As you can see, it doesn't matter how you decide to build/construct/initialize your validators, the only thing that matters is that in the end you have an object that responds to:


And them it will happily blend into the system.

Creating asynchronous validators

Asynchronous validators implementation is pretty much the same as regular validations, there are only 2 differences that you need to be aware of:

  1. Asynchronous validators must respond to the method async returning true
  2. Asynchronous validators must always returns a Promise/A compliant Promise

You can use any Promises/A compliant library to get your promises (when, Q, Promise...) but since we needed to have one internally, and some users may not want to add another dependency, we expose our internal instance of the Promise library for you, so you can just use it if you want.

Let's go for an example:

var cv = require('composed-validations'),
    Promise = cv.Promise;

var delayedValidator = {
  // this is very important, because some validators have different ways of running
  // when composed with async, don't forget it!
  async: function() { return true; };

  test: function(value) {
    // get a hold of this, we gonna need it
    var _this = this;

    return new Promise(function(resolve, reject) {
      setTimeout(function() {
        if (value == 'hello') {
          // if it's ok, you can resolve with anything, it doesn't really matter
        } else {
          // when error happens, raise it! promises style
          reject(cv.error("is not equal to hello", value, _this);
      }, 500);

delayedValidator.test('fail').then(function() {
  // all good, but with the argument that will passed, here will not be reached
}, function(err) {
  // your error handling

One of the reasons that you have to explicitly say that your validator is async, is to protect you on situations like this:

cv.struct() // note this is a "sync" kind of multi validator
  .validate('name', cv.presence()) // ok, presence if sync
  .validate('hello', delayedValidator); // this will raise an error!

Think about it, it's totally possible to convert sync validators into an async form, but it's impossible on the other direction. So, if you add an async validator into a sync multi validator (remember that StructValidator is just a specialized type of MultiValidator) you probably did by mistake, so the library will raise an error and ask you to make your multi validator async:

cv.struct({async: true})
  .validate('name', cv.presence())
  .validate('hello', delayedValidator); // now it's all fine

Built-in Validators

This section documents each single validator on the framework.

First, I'll give you the picture of what the class struct looks like:

Composed Validations Diagram

For the documentation, we gonna separate the validators in three categories:

  • Leaf Validators: those are the validators that operates on most simple values
  • Multi Validators: those are structural validators that helps you to do multiple validations at once
  • Delegational Validators: those are structural validators that will take one other validator and do some kind of structuring on the validator's behavior

Leaf Validators



This validator with check if the given value is present.




var cv = require('composed-validations');
var validator = cv.presence();

// those will throw an error
validator.test("   "); // empty spaces still count as blank

// those are valid, and will not throw an error



This validator tests a value against a Regular Expression.


cv.format(RegExp format);


var cv = require('composed-validations');
var validator = cv.format(/\d+/);

validator.test('ab12'); // ok
validaotr.test('abc'); // error! doesn't match the format!



This validator tests a value against a pre-defined list of options.


cv.include(Array options);


var cv = require('composed-validations');
var validator = cv.include(['one', 'two']);

validator.test('one'); // ok
validator.test('two'); // ok
validator.test('three'); // error, three is not included on the options



This validator if a value is included into a given range.


cv.range(min, max);

Remember that min and max can be pretty much anything, it will work on numbers, but also on strings.

The validator will raise an error on construction if the min value is greater than max.


var cv = require('composed-validations');
var validator = cv.range(-3, 12);

validator.test(-3); // ok, still on the range
validator.test(-4); // error
validator.test(5); // ok
validator.test(13); // error

Multi Validators



This validator enables you to create a group of validations that will run in order to validate a single value.


  async: false

The object with the options on constructor is optional.

Available options:

  • async: if you have ANY async validators into your MultiValidator you must pass this option as true, otherwise when you try to add an async validator it will raise an error. The reason for that is that in order to mix sync and async validators, we must convert all the validators to an async form, also, it changes the way the errors are thrown. When you do a sync validation it will throw the errors right way, on the async scenario they will be dispatched as Promise errors. This flag is to prevent you to use the wrong interface by mistake, so, if you need async on your MultiValidator, send it as true.

Registering validators


This function will register a new validator in the list of validators that are going to run. Remember that all child validators will run, what I mean is, it will not stop on the first failure, when a failure occurs it will register it and keep going to run the rest of the validators, in the end, if there are errors, all of them will be available for you into the error object (also, in case of async, the validators will run in parallel).


A sync example:

var cv = require('composed-validations');
var validator = cv.multi();

// pretend those validators exists for now, they may in future

validator.test(2); // ok

try {
} catch (err) {
  err.message; // a message combining the errors descriptions, good for debug, bad for showing to the user
  err.errors; // a list with each error raised from the validators

An async example:

var cv = require('composed-validations');
var validator = cv.multi({async: true});


validator.test(function() {
  // all ok, do your thing
}, function(err) {
  err.message; // a message combining the errors descriptions, good for debug, bad for showing to the user
  err.errors; // a list with each error raised from the validators



This validator is an extension of the MultiValidator, it has all the features available there, plus a few more.


  async: false

The options are optional, for details on the async option see MultiValidator.

Registering validators

While you still have the add option, these are a few new options that you have to add validators and link them with specific fields on a struct:

validate(field..., validator)

Registers a validator for a given field, and it will automatically wrap the given validator with a FieldValidator associated with the same given field. It register the validator on two lists, the basic validators list (that will run when you call test) and also into the field validators list (check testField method for more info).

This is probably the method that you will use the most, because it address the most common situation (adding a validator to validates the data on a field).

validator.validate('name', cv.presence());
validator.test({name: "someone"});
validator.testField('name'); // will also run the test

addAssociated(field..., validator)

It works almost as same as validate, expect that it will not wrap the validator with a FieldValidator.

// this will end up as same as the previous validate example
validator.addAssociated('name', cv.field('name', cv.presence()));
validator.test({name: "someone"});
validator.testField('name', {name: "someone"}); // will also run the test

addFieldValidator(field..., validator)

It is like addAssociated except that it will not add the validator into the regular validators list, that means the validator will only be called when you ask to validate that specific field, but no the general validation.

validator.addFieldValidator('name', cv.field('name', cv.presence()));
validator.test({name: "someone"}); // this will not trigger any validators
validator.testField('name', {name: "someone"}); // this will run the registered validator for the field

Running validators for a single field

StructValidator makes also possible to only the validators associated with a given field, that can save a lot of work, specially if have some field that uses a resourceful async option, that way on live forms when user updates an input you can run only the validators for that given field.

Remember that the behavior is same as the test method on the regard of sync/async operations, if you use the flag async: true it will return a promise, otherwise will throw an error in case of failure.

How to use it:

var cv = require('composed-validations');
var validator = cv.struct({async: true});

validator.validate('name', 'username', cv.presence());
// lets say this validator does an ajax call to verify if the user name is available
validator.validate('username', uniqUserNameValidator);

// when calling the testField you must pass the entire object to value (not just the
// value of the field), the reason for that is because there are some validators that
// runs a given a field but also needs information from other fields, a
// "password confirmation" validator would be the most common example of that case
validator.testField('name', {name: "", username: ""}).done(function() {
  // the field is fine, do your UI stuff
}, function(err) {
  // err here is a MultiValidationError, as same as the error on the MultiValidator

  var errors = err.errors; // list of errors from the test on that field
  // do your UI updates


var cv = require('composed-validations');

var passwordMatchValidator = {
  test: (value) {
    if (value.password != value.password_confirmation) {
      throw cv.error("Password confirmation doesn't match the password", value, this);

var userValidator = cv.struct();

userValidator.validate('name', 'password', cv.presence());
userValidator.validate('email', cv.format(/\w+@\w+\.\w+/));
userValidator.addAssociated('password_confirmation', passwordMatchValidator);

try {
    name: "",
    email: "invalid",
    password: "123"
} catch (err) {
  err.errors; // a list will all errors // errors on the field name, if there were no errors, will be an empty list



This validator is another kind of MultiValidator but it runs a bit different way.

While MultiValidator is concerned about running all the available validators as quick as possible, and them grouping the errors results, the SequenceValidator instead runs the validators one by one, and if any validation error occurs, it will stop the iteration and throw that error right way.

This behavior is good when you have a slow validation that can be prevented to run when a quicker one can detect the fail first, for example, if you have a validator that hits the server and verify if a given email is already registered on the database, this validation is considered slow because it needs to go into a server, which can take a while, but in the email case, you can prevent it from running if you verify that the email is on an invalid format, that way the format validator can prevent the uniq validator to run until the email format is at least valid.

Another difference on SequenceValidator is that on it, it's possible to transform the given value for the next validator. That enables possibilities like a HttpValidator that will fetch data into a server, and them send it to the next validator that will work on the returned value.

For that matter, ALL of the built-in validators will always return the same input that is given to them, when writing validators you must do that too, unless you really writing a validator about transforming data.


  async: false

The options are optional, for details on the async option see MultiValidator.


// let's supposed this is some library that does a request and checks something
var checkRemoteNumber = require('check-remote-number')

var idValidator = cv.sequence({async: true})

idValidator.test("ha"); // will fail on the format validator, will not call teh service
idValidator.test("123"); // format ok, checking on the server

Delegational Validators



The field validator will run a given validator into a specific field of an object.


cv.field(field, validator, {
  optional: false


  • field: the field name
  • validator: the validator to run the given field
  • options:
    • optional: if true, the validator will accept when the field name is not present on the object, (that means, when the object responds false to hasOwnProperty(field))


var cv = require('composed-validations');
var validator = cv.field('name', cv.presence(), {optional: true});

// will fail because it can't access fields on null (same for false or undefined)

// will pass, since it's optional and the field is not present

// will fail because the field is present, so the it will validate the presence, and fail
validator.test({name: null});

// ok
validator.test({name: "chick"});



The negate validator will invert the result of a given validator.




var cv = require('composed-validations');
var validator = cv.negate(cv.presence());

validator.test('hey'); // will fail, inverting the presence validator result
validator.test(null); // ok


By a current design constraint, the error messages that comes from NegateValidator are not user friendly... They look like this: validation negated failed (all the times). This is something I plan to improve over time, but for now I suggest you to use the RephraseValidator to define a better error message for your users.



Given the value is a list, runs the validator against of the items, if any item fails the validation, a ValidationError will be thrown.




var cv = require('composed-validations');
var validator = cv.all(cv.presence());

validator.test([]); // empty lists give no errors
validator.test([1, null, 'ok']); // fails because null is rejected by PresenceValidator
validator.test(['a', {}, 3]); // all ok here



Changes the error from a given validator when it fails.


cv.rephrase(newMessage, validator)


var cv = require('composed-validations');
var validator = cv.rephrase('feed me something true dude...', cv.presence());

try {
} catch (err) {
  err.message; // 'feed me something true dude...'

Helper Library

This is me sharing the internals of composed-validations with you, I think since they were useful for me, and you are going to load them anyway, they might be helpful for you too.

The utility functions listed here are available at the _ variable into the main composed-validations require (like the good guys underscore and lodash:

var _ = require('composed-validations')._;

On the examples I'll consider that you have the _ variable set as on the code above.

So here is goes the list of available functions, pick what servers you.


Stringify an object. This is just an alias for JSON.stringify

_.json('a'); // "a"


Detects if a given value is a string.

_.isString('a'); // true
_.isString("ab"); // true
_.isString(""); // true
_.isString([]); // false
_.isString(null); // false
_.isString({}); // false


Detects if a given value is a function.

_.isFunction(function() {}); // true


Detects if a given value is an array.

_.isArray([]); // true
_.isArray([1, 3]); // true
_.isArray(""); // false
_.isArray({}); // false


Detects if a given value is a validator (that means, it has a property test that is a Function)

_.isValidator(cv.presence()); // true
_.isValidator({}); // false


This function will raise an error unless the given value is a validator.


Will throw an error unless the given value is an instance of ValidationError (extensions of the class are also accepted).

contains(list, value)

Check if value is present into the list.

_.contains([1, 2, 3], 1); // true
_.contains([1, 2, 3], 5); // false

map(list, iterator)

Given a list, returns a new list by iterating over the elements with the given iterator.[1, 2, 3], function (x) {
  return x * 2;
}; // [2, 4, 6]

reduce(list, initial, iterator)

_.reduce([1, 2, 3], 0, function (acc, x) {
  return acc + x;
}); // 6


Given a function, make it returns a rejected Promise if any error is thrown, otherwise returns Promise that resolves with the function returned value.

var fn = function(x) { return 3 + x; };
var lifted = _.lift(fn);

lifted(2).then(function(z) {
  alert(z); // 5


Given a string name, converts underlines into spaces and uppercase the first letter.

_.humanizeFieldName('name'); // Name
_.humanizeFieldName('password_confirmation'); // Password confirmation

More Information

If you wanna know more tricks and tips about composed-validations check our Wiki Pages.

Current Tags

  • 0.8.1                                ...           latest (5 years ago)

11 Versions

  • 0.8.1                                ...           5 years ago
  • 0.8.0                                ...           6 years ago
  • 0.7.1                                ...           6 years ago
  • 0.7.0                                ...           6 years ago
  • 0.6.0                                ...           6 years ago
  • 0.5.0                                ...           6 years ago
  • 0.4.0                                ...           6 years ago
  • 0.3.0                                ...           6 years ago
  • 0.2.0                                ...           6 years ago
  • 0.1.0                                ...           6 years ago
  • 0.0.0                                ...           6 years ago
Maintainers (1)
Today 0
This Week 0
This Month 0
Last Day 0
Last Week 0
Last Month 0
Dependencies (2)
Dev Dependencies (2)
Dependents (2)

Copyright 2014 - 2016 © |