Validate JS objects just by example, not schema
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Koogn

Schema-less validation for JavaScript

Introduction

Sooner or later you're gonna need to somehow verify that the data you're working with conforms to what you expect them to be like. For example, that the email submitted to your API endpoint has proper format or that the value that should be a number doesn't receive a string.

There's a plenty of great libraries for exactly that but all of them needs you to create some kind of blueprint, a schema describing the structure of the data.

Koogn works differently. Instead of validating data (let's say a javascript object) against a schema, it compares it to just another javascript object - an example. Koogn is smart, so it can analyze structure of your example object and object you want to validate to make proper comparison.

Advantages

  • Very simple to use
  • You don't need to define schema, just use some example data
  • Most of the time you even don't need to prepare the example. You probably already have it. Your example data is the data you are testing your program/API/whathever with or the output it generates.
  • If you ever find yourself in need of a bit more complex validation scenarios, it's easy to extend your example using a simple syntax to get what you need.
  • There's no performance drawbacks for all these features (see more on that bellow)
  • Just by looking at it, the example data clearly communicates how the data should look like

Example

Let's say we want to validate this object:

const book = {
  title: 'Saved by Koogn',
  authors: ['David Ruzicka'],
  releaseDate: '2018-02-03',
}

The only thing that we need is another object. example - the ethalon by which we will compare the book object.

const {isValid} = require('koogn').createValidator()

const example = {
  title: 'Example',
  authors: ['John Smith', 'Joe Noel'],
  releaseDate: '1967-10-24',
}

isValid(example, book) // returns true

We've determined that the book object is valid. The structure is the same, types of the properties are the same and the format of releaseDate field in both cases is the date.

Just for comparison: To validate exactly the same things using JSON schema requires you to define schema like this:

const schema = {
  type: 'object',
  properties: {
  title: {
    type: 'string',
      required: true
  },
  authors: {
    type: 'array',
      items: {
      type: 'string',
        required: true
    },
    required: true
  },
  releaseDate: {
    type: 'string',
      format: 'date',
      required: true
  }
}

Usage

First install Koogn and save it to your project

npm install koogn --save

Then require the package and create validator instance. There are two ways how to do that:

const validator = require('koogn').createValidator()

or

const Validator = require('koogn').Validator
const validator = new Validator()

Both createValidator function and Validator constructor can receive configuration object to tweak validator behavior (more on that bellow)

Once you have an validator instance you can use one of these methods to perform validation.

validate(example, instance) performs validation of instance against provide example and returns full validation report.

isValid(example, instance) performs validation of instance against provide example and returns simple true/false if instance is valid or not.

throwIfNotValid(example, instance) performs validation of instance against provide example and if instance is not valid, throws an ValidationError.

const validator = require('koogn').createValidator()

const bookExample = {
  title: 'Example',
  authors: ['John Smith', 'Joe Noel'],
  releaseDate: '1967-10-24',
}

const instance = {
  title: 'Saved by Koogn',
  authors: ['David Ruzicka'],
  releaseDate: '2018-02-03',
}

validator.validate(bookExample, instance)

validator.isValid(bookExample, instance)

validator.throwIfNotValid(bookExample, instance)

All three of those methods can also return validation function with first parameter already pre-applied. Using it this way is also more performant solution as the conversion from example object to internal schema needs to happen just once. Let's demonstrate on isValid:

const isValidBook = validator.isValid(bookExample)  // create test function

isValidBook(instance)

Optional / required properties

By default all properties in provided example object are considered to be required. In case you want some of your object properties to be optional, you can use reserved property $optional and pass property name that should be optional or the array of them:

validator.validate({
    id: 1, 
    author: 'john',     // optional property
    title: 'The Book',  
    year: 1940,         // optional property
    $optional: ['year', 'author']
}, yourData)

If you find your object to have more optional properties than required ones, use $required instead. This changes default behaviour and assumes every property is now optional except the ones specified in $required.

validator.validate({
    id: 1,            // the only required field
    author: 'john',
    title: 'The Book',
    year: 1940,
    $required: 'id'
}, yourData)

More complex validations

Chances are that your project starts with only simple validation needs. But as your project grows it may be necessary to handle more complex validation scenarios. Although Koogn is mainly intended for simple validation, it can handle even complex validations by utilizing reserved key $schema. Through it you can define full jsonschema for the property with all the features supported by jsonschema

In the example bellow validation of labels property is completely overriden by provided schema:

{
  id: 11,
  name: 'john',
  labels: {
    $schema: {
      type: 'array', 
      items: {
        type: 'string',
        minLength: 2,
        maxLength: 100
      }
    }
  },
}

Configuration

There's a number of options through which you can configure validator. These are default values:

const options = {
  arrays: {
    mode: 'all', // first|uniform|all 
  },
  strings: {
    formatDetectionMode: 'both', // none|name|content|both
  },
  objects: {
    additionalProperties: false, // false|true
  },
}

Options should be passed as a parameter to createValidator function

const {createValidator} = require('./lib/validator')
const validator = createValidator({arrays: {mode: 'first'}})

or as a parameter to a Validator constructor:

const {Validator} = require('./lib/validator')
const validator = new Validator({arrays: {mode: 'first'}})

Whatever you like better

arrays options

arrays.mode (all|first|uniform default is all)

This option has effect only on arrays containing two or more items

first - This option takes into account just the first item in any array Rest is ignored.

uniform - This option makes sure that if there are more items all of them shares the same type and structure. if not, it throws an error.

all - If provided example object contains array of items with mutually incompatible types/structures, parser will try to come up with least common type/structure and validate against that. It works in a natural way.

If your example object contains array of items sharing the same type, than validator imposes that type restriction on array items:

const {isValid} = require('./lib/validator').createValidator({arrays: {mode: 'all'}})
const example = [1, 3, 4]

isValid(example, [1, 2])      // true
isValid(example, ['a', 'b'])  // false
isValid(example, [1, 2, 'a']) // false
isValid(example, {a: 1})      // false

If your example object contains array of mixed numbers and strings, validator assumes that such an array can contain mixture of types so it doesn't impose type restriction on array items:

const {isValid} = require('./lib/validator').createValidator({arrays: {mode: 'all'}})
const example = ['str', 3, 4]

isValid(example, [1, 2])      // true
isValid(example, ['a', 'b'])  // true
isValid(example, [1, 2, 'a']) // true
isValid(example, {a: 1})      // false

If your example object contains array of objects that shares the same structure. Only objects having the same structure will pass validation

const {isValid} = require('./lib/validator').createValidator({arrays: {mode: 'all'}})
const example = [
  {a: 1, b: 'str'},
  {a: 56, b: 'something'}
]

isValid(example, [{a: 3, b: 'xxx'}, {a: 588, b: 'aaa'}])  // true
isValid(example, [{a: 3, b: 'xxx'}, {a: 588}])            // false (second item is missing property 'b')
isValid(example, [{a: 3, b: 'xxx'}, {a: 588, b: 11}])     // false (b of second item is not string)
isValid(example, [{a: 3, b: 'xxx'}, 22])                  // false (second item is not object)
isValid(example, ['a', 'b'])                              // false (none of the items is object)

If your example object contains array of objects that doesn't share the same structure. Than the only restriction applied on array items is to be an object

const {isValid} = require('./lib/validator').createValidator({arrays: {mode: 'all'}})
const example = [
  {a: 1, b: 'str'},
  {a: 56, c: [1]} // structure is different than first item
]

isValid(example, [{a: 3, b: 'xxx'}, {a: 588, b: 'aaa'}])  // true
isValid(example, [{a: 3, b: 'xxx'}, {a: 588}])            // true (structure doesn't matter)
isValid(example, [{a: 3, b: 'xxx'}, {a: 588, b: 11}])     // true (structure doesn't matter)
isValid(example, [{a: 3, b: 'xxx'}, 22])                  // false (second item is not object)
isValid(example, ['a', 'b'])                              // false (none of the items is object)

If your example object contains array of items sharing the same type, than validator imposes that type restriction on array items:

objects options

objects.additionalProperties (true|false default is false)

If this option is set to true then object having extra properties than example object will still be validated

strings options

strings.formatDetectionMode (none|name|content|both default is both)

none - Validator will make no attempt to detect format of strings in provided example object

name - If string value in provided example object matches one from the list bellow, restriction for that format will apply.

{
  prop01: 'date',         // '2012-07-08'
  prop02: 'time',         // '16:41:41'
  prop03: 'date-time',    // '2012-07-08T16:41:41.532Z' (and variants)
  prop04: 'utc-millisec', // '1234567890'
  prop05: 'regex',        // '/a/'
  prop08: 'color',        // '#ff0000'
  prop09: 'style',        // 'color: red;'
  prop10: 'phone',        // '+31 42 123 4567'
  prop11: 'email',        // 'john@smith.com'            
  prop12: 'ip-address',   // '192.168.0.1'
  prop13: 'ipv4',         // '192.168.0.1'
  prop14: 'ipv6',         // 'fe80::1%lo0'
  prop15: 'uri',          // 'http://www.google.com/'
  prop16: 'host-name',    // 'www.google.com'
  prop17: 'hostname',     // 'www.google.com'
  prop18: 'alpha',        // 'abracadabra'
  prop19: 'alphanumeric', // 'abracadabra123'
}

example:

const {isValid} = require('./lib/validator').createValidator({arrays: {stings: 'name'}})
const example = {updatedAt: 'date-time'}

isValid(example, {updatedAt: '2012-07-08T16:41:41.532Z'})  // true
isValid(example, {updatedAt: 'hello'})                     // false
isValid(example, {updatedAt: 11})                          // false

content - Similar to name option but format is autodetected from the value itself example:

const {isValid} = require('./lib/validator').createValidator({arrays: {mode: 'content'}})
const example = {updatedAt: '2018-01-01T20:15:31.532Z'}

isValid(example, {updatedAt: '2012-07-08T16:41:41.532Z'})  // true
isValid(example, {updatedAt: 'hello'})                     // false
isValid(example, {updatedAt: 11})                          // false

both - Combination of both name and content options example:

const {isValid} = require('./lib/validator').createValidator({arrays: {mode: 'content'}})
const example = {
  updatedAt: '2018-01-01T20:15:31.532Z',
  createdAt: 'date'
}

isValid(example, {updatedAt: '2012-07-08T16:41:41.532Z', createdAt: '2011-10-01'}) // true
isValid(example, {updatedAt: 'hello', createdAt: '2011-10-01'})                    // false
isValid(example, {updatedAt: '2012-07-08T16:41:41.532Z', createdAt: 'hello'})      // false