Asynchronous validation for node and the browser

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Async Validate

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Asynchronous validation for node and the browser. It has minimal dependencies and uses a plugin architecture so you only need to include the plugins for types you want to validate and can easily create your own validation plugins.
Examples are in EXAMPLE and the example directory.
- Descriptor - Rules - Errors - Plugins - Validation - Messages - Transform - API - Test - Spec - Cover - Lint - Browser - Clean - Docs - Example - Readme


npm i async-validate


Define validation rules, assign them to a schema using the necessary plugins and call validate:
var Schema = require('async-validate')
  , descriptor = {
      type: 'object',
      fields: {
        name: {type: "string", required: true}
  , schema = new Schema(descriptor)
  , source = {};


schema.validate(source, function(err, res) {
  if(err) {
    throw err; 
  }else if(res) {
    // validation failed, res.errors is an array of all errors
    // res.fields is a map keyed by field unique id (eg: ``)
    // assigned an array of errors per field
    return console.dir(res.errors)
  // validation passed



A descriptor is a collection of validation rules as a map of fields to rules, rules may be declared as an object, array or function.

Object Definition

var descriptor = {
  type: 'object',
  fields: {
    name: {type: 'string', required: true}

Array Definition

You may declare an array to use multiple validation rules per field, see multiple rules.

Function Definition

Use an inline function definition for application specific rules, see inline rule.

Composite Definition

To share common fields across different schemas move them to a module and require them.
Module to represent an address field:
module.exports = {
  type: 'object',
  fields: {
    name: {type: 'string', required: true},
    street: {type: 'string', required: true},
    city: {type: 'string', required: true},
    zip: {type: 'string', required: true}

Muliple objects containing an address field that need the same validation rules:
var address = require('./address')
  , user = {
      type: 'object',
      fields: {
        address: address
  , invoice = {
      type: 'object',
      fields: {
        bill: address


function rule(cb)

Rules are functions that perform validation of a value, they are invoked in the scope of a rule instance (file, api docs).
A rule function can access all relevant properties and methods using this and should raise an error if this.value fails a validation test, see errors. Rule functions may raise multiple errors for different validation failures.
The plugin rule method of declaring rule functions is preferred as it is the most modular.

Inline Rule

The rule function is assigned directly to the field:
var descriptor = {
  type: 'object',
  fields: {
    id: function(cb) {
      // if this.value has error condition call this.raise() 

Assigned Rule

Assigned to the test field so that you may pass data from the rule to the function:
var descriptor = {
  type: 'object',
  fields: {
    id: {
      foo: 'bar',
      test: function(cb) {
        // if this.value has error condition call this.raise() 

Plugin Rule

Plugin that assigns the rule function as a static method.
Create a plugin module:
module.exports = function() {
  // declare static rule function with name `id` = function id(cb) {
    // if this.value has error condition call this.raise() 

Load and use the plugin:
var Schema = require('async-validate');
var descriptor = {
  type: 'object',
  fields: {
    id: {type: 'id'}

The static id method will then be invoked for every rule of type id, this is the most portable style as it enables easily moving validation rules into modules and packages that may be shared.

Multiple Rules

It is often useful to test against multiple validation rules for a single field, to do so make the rule an array of objects, for example:
var descriptor = {
  type: 'object',
  fields: {
    email: [
      {type: "string", required: true},
      function(cb) {
        // test if email address (this.value) already exists 
        // in a database and call this.raise() if it does

Deep Rules

If you need to validate deep object properties you may do so for validation rules that are of the object or array type by assigning nested rules to a fields property of the rule.
var descriptor = {
  type: 'object',
  fields: {
    name: {type: "string", required: true},
    address: {
      type: "object",
      required: true,
      fields: {
        street: {type: "string", required: true},
        city: {type: "string", required: true},
        zip: {type: "string", required: true, len: 8, message: "invalid zip"}
var schema = new Schema(descriptor);
schema.validate({address: {}}, function(err, res) {
  // res.errors contains errors for name, street, city, zip

Note that if you do not specify the required property on the parent rule it is perfectly valid for the field not to be declared on the source object and the deep validation rules will not be executed as there is nothing to validate against.
The parent rule is also validated so if you have a set of rules such as:
var descriptor = {
  type: 'object',
  fields: {
    roles: {
      type: "array",
      required: true,
      len: 3,
      fields: {
        0: {type: "string", required: true},
        1: {type: "string", required: true},
        2: {type: "string", required: true}

And supply a source object of {roles: ["admin", "user"]} then two errors will be created. One for the array length mismatch and one for the missing required array entry at index 2.


This section describes the recognised rule properties and their behaviour, if you are using an assigned rule or plugin rule you can define properties on the rule object and they are available to the rule function via this.
See the system schema.
Type Identifier
  • type <string|function|array>: Type identifier, constructor function or list of types.

The type property indicates the type of rule to use, a type corresponds to a plugin function and the plugin should have been loaded.
A type identifier is required if the rule is not an inline or assigned rule.
Recognised type values are:
  • array: Must be an array as determined by Array.isArray.
  • boolean: Must be of type boolean.
  • date: Value must be valid as determined by moment().isValid().
  • enum: Value must exist in the list.
  • float: Must be of type number and a floating point number.
  • function: Must be of type function.
  • integer: Must be of type number and an integer.
  • null: Must strictly equal null.
  • number: Must be of type number.
  • object: Must be of type object and not Array.isArray.
  • regexp: Must be an instance of RegExp or a valid string regexp.
  • string: Must be of type string.

When the object plugin has been loaded the type field may be a function in which case the value must be an instanceof the function assigned to type.
To allow a field to be of multiple types you may declare an array of valid type identifiers, for example:
{type: ['string', String, Number], required: true}
  • list <array>: The list of enumerable values.

To validate a value from a list of possible values use the enum type with a list property containing the valid values for the field, for example:
var descriptor = {
  type: 'object',
  fields: {
    role: {type: "enum", list: ['admin', 'user', 'guest']}
Date Format
  • format <string>: Date format string.
  • local <boolean>: Use local time rather than UTC.

Validating dates can be complex but using moment date validation is substantially easier.
If no format is specified for a rule that is a date type then it is assumed the date is ISO 8601. If a format is specified then the date is validated according to the specified format.
It is recommended you read the moment documentation on the isValid method to understand what validation is performed.
The important part is:
Note: It is not intended to be used to validate that the input string matches the format string. Because the strictness of format matching can vary depending on the application and business requirements, this sort of validation is not included in Moment.js.

This limitation may be overcome by combining a pattern in a date rule, for example:
var descriptor = {
  type: 'object',
  fields: {
    active: {
      type: "date",
      format: "YYYY-MM-DD",
      pattern: /^([\d]{4})-([\d]{2})-([\d]{2})$/
  • message <string|function>: Custom error message.

The message property defines the error message when validation fails, it overrides any default message. The property may be a string or function, see messages.
  • required <boolean>: Field is required flag.

The required property indicates that the field must exist on the source object being validated.
  • additional <boolean>: Determines if additional properties are allowed.

When a rule is of the object type and additional is set to false an error is raised if the source object contains any properties not in the schema.
  • fields <object>: Map containing rules for object properties.

Rules of the object and array type may declare a fields object which creates a nested schema, see deep rules.
  • pattern <regexp>: Pattern match regular expression.

The pattern property is a regular expression that the value must match to pass validation.
  • placeholder <function>: Placeholder function.

A function that may return a default value for a field, it is invoked when the field value is undefined and the return value is assigned to the property.
  • min <integer>: Minimum length value.
  • max <integer>: Maximum length value.

A range is defined using the min and max properties. For string, function and array types comparison is performed against the length, for number types the number must not be less than min nor greater than max.
  • len <integer>: Length constraint.

To validate an exact length of a field specify the len property. For string, function and array types comparison is performed on the length property, for the number type this property indicates an exact match for the number, ie, it may only be strictly equal to len.
If the len property is combined with the min and max range properties, len takes precedence.
  • values <array>: Array of rules for array types.

Used with the array type as a shorthand for validating array values, may be an object or array containing validation rules.
When values is an object it is applied to all array elements in the source array otherwise each values entry is compared against each source array entry which allows mixed types to be used in arrays.
Note that values is expanded to fields, see deep rules.
  • match <regexp>: Expands a rule to multiple properties.

The match property may be used to apply a rule to multiple properties of the same object, the rule is cloned for each property name that matches the regular expression and applied to the matched property.
In this scenario specifying required on the match rule would be a non-operation.
This is useful when you have a sequence of properties that share the same rules:
{match: /^address[1-3]$/, type: 'string'}
  • resolve <function>: Rule location function.

A function that may be declared to conditionally determine the rule to use for a given object, if is invoked synchronously in the scope of the object being validated. It should inspect the object and return a rule to use for that particular object.
This is typically used to allow rules to be conditional on a property of an object, for example an object may have a type field that determines the type or class of object and validation needs to change for the different types.
  • test <function>: Rule function.

The function to use for rule validation.
  • whitespace <boolean>: Determines if whitespace input should be an error.

It is typical to treat required fields that only contain whitespace as errors. To add an additional test for a string that consists solely of whitespace add a whitespace property to a rule with a value of true. The rule must be a string type.
You may wish to sanitize user input instead of testing for whitespace, see transform for an example that would allow you to strip whitespace.


To raise an error in a validation rule call raise, the signature for raise is equivalent to util.format except that it may also accept a Reason as the first argument.
function id(cb) {
  if(!/^[a-z0-9-]+$/i.test(this.value)) {
    this.raise('%s is not a valid id', this.field); 

Decorate the error with a reason:
function id(cb) {
  if(!/^[a-z0-9-]+$/i.test(this.value)) {
      this.reason('id', {level: 'warn'}),
      '%s is not a valid id',

Adding a reason allows associating an identifier with an error and optional meta data about the error which can be useful if you need to associate a severity with errors to distinguish between error types.
To signal that an internal processing error has occured pass an Error to the callback, for example:
function id(cb) {
  this.model.findById(this.value, function(err, id) {
    if(err) {
      return cb(err); 
    // validate id for error conditions


Plugins are modules defining functions that allow users to only load functionality specific to the rule types being used which allows builds for the browser to be as lean as possible.
See zephyr for plugin system documentation.

Loading Plugins

To load all plugins:

It is preferable to only use plugins for the types you are using:
var Schema = require('async-validate');

Creating Plugins

Static plugins are mapped to type identifiers and instance plugins may be used to extend Rule which is useful for sharing functionality across rule plugins, see the util plugins.
See plugin rule for an example and plugin contains the plugins that ship with this package.
The important point to remember is that for helper methods assign to this and for static rule functions (located by type) assign to this.main in the plugin.
Helper method:
module.exports = function() {
  // create a helper method on the prototype
  // of the class used for static function scope
  this.helper = function(value) {
    return value;

Static method:
module.exports = function() { = function id(cb) {
    // use helper method
    var val = this.helper(this.value);
    // implement validation for `id` type

Helper Plugins

The following helper plugins ship with this package, you can use them all with:
function pattern()

Validate using a regexp pattern, typically invoked from a rule function, raises an error if a value fails to match a rule regexp pattern.
function range()

Validates that a value falls within a given range or is of a specific length, typically invoked from a rule function, raises an error if a value is out of bounds.
function required()

Validate a required field, typically invoked from a rule function, raises an error if a required field is not present.
function type()

Validate a value is one of the expected type(s), typically invoked from a rule function, raises an error if the value is not one of the declared types.


This section describes using the processing options available when calling validate.


To callback early on the first value that generates a validation error and only report a single error use the bail option. This is useful when a user interface only needs to show the first error condition or if continuing processing would add unnecessary overhead.
Remember that a rule can generate multiple validation errors so if you need more fine grained control you can use the single and first options.


Sometimes it is useful to pass existing data into all rule functions as transient data so that your rule functions may reference existing code for performing async operations. A common use case would be using a model class to query a database and then validate on the returned data.
To do this you may use the vars processing option when calling validate.
The value should be an Object; each property of the vars object is passed into the Rule scope so that they are available via this.
Be aware that if you use a built in field (see Rule) it will be overwritten.
See the vars test and model fixture for an example.


To pass state information use this.state in test functions, set the state option to specify an alternative object to use for the initial state. When no state is given the empty object is used.
See the state example.


Depending upon your application requirements, you may need i18n support or you may prefer different validation error messages.
The easiest way to achieve this is to assign a message to a rule:
{name:{type: "string", required: true, message: "Name is required"}}

You may also use a function for the rule message, it is invoked in the scope of the Rule and passed the original message and replacement parameters:
var descriptor = {
  type: 'object',
  fields: {
    name: {
      type: "string",
      required: true,
      message: function(message, parameters) {
        return this.field + ' is required';

If you just want to change the default messages:
var Schema = require('async-validate')
  , messages = require('async-validate/messages')
  , descriptor = {
      type: 'object',
      fields: {
        name:{type: "string", required: true}}
  , schema;
messages.required = "%s is a required field";
schema = new Schema(descriptor, {messages: messages});

Potentially you may require the same schema validation rules for different languages, in which case duplicating the schema rules for each language does not make sense.
In this scenario you could just require your own messages file for the language and assign it to the schema:
var Schema = require('async-validate')
  , messages = require('messages-es')
  , descriptor = {
      type: 'object',
      fields: {
        name:{type: "string", required: true}}
  , schema = new Schema(descriptor, {messages: messages});

If you are defining your own rule functions it is better practice to assign the message strings to a messages object and then access the messages via the this.messages property within the function.


Sometimes it is necessary to transform a value before validation, possibly to coerce the value or to sanitize it in some way. To do this add a transform function to the validation rule. The property is transformed prior to validation and re-assigned to the source object to mutate the value of the property in place.
Without the transform function validation would fail due to the pattern not matching as the input contains leading and trailing whitespace, but by adding the transform function validation passes and the field value is sanitized at the same time.
var Schema = require('..')
  , descriptor = {
      type: 'object',
      fields: {
        name: {
          type: "string",
          required: true, pattern: /^[a-z]+$/,
          transform: function(value) {
            return value.trim();
  , schema = new Schema(descriptor)
  , source = {name: " user  "};


schema.validate(source, function() {



function Schema(rules, [opts])

Encapsulates the rules associated with a schema and the logic for performing validation.
  • rules: The schema rules.
  • opts: Configuration options.

  • messages: An alternative messages object for the schema.
function messages([messages])

Get or set the messages associated with the schema.
function validate(source, [opts], cb)

Validates a source object against the schema rules.
  • source: The object to validate.
  • opts: Map of processing options for the validation.
  • cb: Callback function to invoke when validation completes.

  • first: Invoke callback when the first validation rule generates an error.
  • single: Only ever return a single error.
  • bail: Shorthand for single and first.
  • messages: Overrides the schema messages.
  • parallel: A boolean indicating that the validation should be executed in parallel.
  • field: Field name for the source object, default is source when not specified.
  • parent: Parent object for the source value.
  • state: Object to be used as the initial user data state.
  • vars: Object map of variables to assign to each rule.
  • literal: If true do not use parameter replacement for messages, pass through literally.
function plugin(plugins)

Static plugin loader method; accepts an array of plugin functions.
function clone(source, [target])

Static clone; deep copies simple objects and arrays, RegExp instances are passed by reference.


function Rule(opts)

Encapsulates the data associated with a validation rule and the value to be validated. Rule functions are invoked in the scope of a Rule instance which exposes the following public fields:
  • rule: The validation rule in the schema descriptor.
  • value: The value of the property being validated.
  • field: The name of the property being validated.
  • parent: The parent object that declares the property.
  • source: The source object passed to validate().
  • messages: Reference to the schema messages.
  • errors: Array of errors for the field validation.
  • state: User data for validation state.
  • reasons: Map of default error reasons.
function isRoot()

Determine if validation is being performed against the root source object.
function reason(id, [opts])

Create a reason for a validation error, returns a Reason instance suitable for passing as the first argument to raise.
function raise([reason], message, ...)

Adds an error message to the list of errors encountered during validation of a value.
The first argument may optionally be a Reason instance returned by reason() allowing a user to associate an identifier with the validation error and optional meta data. An error raised with a Reason has a reason field referencing the supplied reason.
When replacement parameters are supplied the behaviour is identical to util.format.
function format(message, ...)

Format a message with replacement parameters like util.format.
Useful when a rule declares message as a function and wishes to construct the error message with parameters.
function validates()

Returns a boolean derived from the rule required property and other factors to determine if the value should be subject to validation.
function diff(expected, received)

Compare two arrays, return false if they are equal otherwise return an array that is the difference between the supplied arrays.


The errors created by raise are assigned the following public fields:
  • key: Unique key for the error, eg:
  • field: The name of the property that failed validation.
  • value: The value of the property.
  • parent: The parent object that declares the property.
  • reason: A Reason for the error when available.


function Reason(id, [opts])

Represents the reason for a validation error, may be created using reason().
You must supply a reason id; if opts are passed they are assigned as properties of the reason instance. When toString() is called on a Reason instance the id is returned.


Clone the repository, install project and global dependencies (mdp, jshint and jscs):
npm i && npm i -g mdp jshint jscs


Run the test specifications:
npm test


Compile test specifications for the browser (open test/index.html):
npm run spec


Generate code coverage:
npm run cover


Run the source tree through jshint and jscs:
npm run lint


Create a standalone browserify build:
npm run browser


Remove generated files:
npm run clean


To generate all documentation:
npm run docs


Generate EXAMPLE (requires mdp):
npm run example 


Generate the readme file (requires mdp):
npm run readme


Everything is MIT. Read the license if you feel inclined.
Created by mkdoc on February 27, 2017