casual vs chance vs faker vs randexp

Synthetic Data Generation Libraries for JavaScript

casual, chance, faker, and randexp are JavaScript libraries used to generate synthetic data for development, testing, and prototyping. casual, chance, and the actively maintained @faker-js/faker provide semantic fake data generators for common entities like names, addresses, and emails, while randexp specializes in producing random strings that match a given regular expression pattern. These tools help developers create realistic mock data without exposing real user information.

Npm Package Weekly Downloads Trend

3 Years

Github Stars Ranking

Stat Detail

Package	Downloads	Stars	Size	Issues	Publish	License
Package	Downloads	Stars	Size	Issues	Publish	License
casual	0	3,017	-	41	7 years ago	MIT
chance	0	6,557	2.13 MB	177	9 months ago	MIT
faker	0	-	10.1 MB	-	-	MIT
randexp	0	1,871	-	14	8 years ago	MIT

Synthetic Data Generation in JavaScript: casual vs chance vs faker vs randexp

When building modern web applications, developers often need realistic-looking test data — for UI demos, automated tests, or local development environments. The JavaScript ecosystem offers several libraries to generate synthetic data, each with distinct philosophies and capabilities. Among them, casual, chance, faker, and randexp stand out, but they solve different parts of the problem. Let’s examine how they compare in real-world usage.

🧪 Core Purpose: What Each Library Actually Does

casual, chance, and faker are general-purpose fake data generators. They produce structured values like names, addresses, emails, dates, and more. randexp, by contrast, is a specialized tool that generates random strings matching a given regular expression — it doesn’t know what a "phone number" is, but it can produce strings that look like one if you give it the right pattern.

This fundamental difference means randexp often complements the others rather than competing directly.

// casual: Built-in semantic generators
import casual from 'casual';
const name = casual.full_name; // "John Doe"
const email = casual.email;   // "john.doe@example.com"

// chance: Similar semantic API
import Chance from 'chance';
const chance = new Chance();
const name = chance.name();     // "Emma Thompson"
const email = chance.email();   // "emma.thompson82@example.org"

// faker: Rich, locale-aware data
import { faker } from '@faker-js/faker';
const name = faker.person.fullName(); // "Robert Johnson"
const email = faker.internet.email(); // "robert.johnson@acme.net"

// randexp: Pattern-based string generation only
import RandExp from 'randexp';
const phone = new RandExp(/\d{3}-\d{3}-\d{4}/).gen(); // "555-123-4567"

🌍 Locale and Internationalization Support

If your application serves users in multiple countries, locale support becomes critical.

faker (specifically the community-maintained @faker-js/faker) offers extensive localization. You can switch locales on the fly and even mix them:

import { faker } from '@faker-js/faker';
faker.locale = 'de';
console.log(faker.person.fullName()); // "Müller, Anna"

faker.setLocale('ja');
console.log(faker.person.fullName()); // "田中 花子"

casual includes some non-English data (like Russian names) but lacks a formal locale-switching mechanism. You’re mostly stuck with English defaults unless you manually override providers.

chance has minimal built-in internationalization. While you can seed dictionaries, there’s no official support for alternate locales.

randexp is inherently locale-agnostic — since it works from regex patterns, it can generate any character set you define, but you must craft the pattern yourself.

🔁 Seeding and Reproducibility

Deterministic test runs require seeded randomness so that the same input always produces the same output.

chance makes seeding straightforward:

import Chance from 'chance';
const chance1 = new Chance(123);
const chance2 = new Chance(123);
console.log(chance1.name() === chance2.name()); // true

faker also supports seeding via its .seed() method:

import { faker } from '@faker-js/faker';
faker.seed(123);
console.log(faker.person.fullName()); // Always the same

casual allows seeding through its global seed() function:

import casual from 'casual';
casual.seed(123);
console.log(casual.full_name); // Consistent across runs

randexp does not expose a seed API. Because it relies on JavaScript’s Math.random(), results aren’t reproducible unless you monkey-patch the global random function — which isn’t recommended in production code.

🧩 Extensibility and Custom Data

All three general-purpose libraries let you define custom generators, but their approaches differ.

casual uses a provider registration system:

import casual from 'casual';
casual.define('product_name', () => `${casual.word} ${casual.word}`);
console.log(casual.product_name); // "Solar Widget"

chance lets you add mixins:

import Chance from 'chance';
const chance = new Chance();
chance.mixin({
  product_name() {
    return `${this.word()} ${this.word()}`;
  }
});
console.log(chance.product_name()); // "Quantum Gadget"

faker supports module extension through direct assignment:

import { faker } from '@faker-js/faker';
faker.product = {
  name: () => `${faker.word.adjective()} ${faker.word.noun()}`
};
console.log(faker.product.name()); // "Innovative Solution"

randexp doesn’t need extensibility in the same way — you just write a new regex. However, complex patterns can become hard to maintain.

⚠️ Maintenance Status and Deprecation Warnings

As of 2024, casual is effectively unmaintained. Its npm page shows no recent updates, and the GitHub repository hasn’t seen meaningful activity in years. While it still works, it should be avoided in new projects.

chance is in maintenance mode. The author states it’s “feature complete” and only accepts critical bug fixes. It’s stable but unlikely to evolve.

faker (the original faker package) was deprecated in early 2022. The community fork @faker-js/faker is now the active, well-maintained successor. Any reference to “faker” in modern contexts should mean this fork.

randexp remains actively maintained, with recent updates addressing security and compatibility.

🛑 Important: Do not install the original faker package (npm install faker). Use @faker-js/faker instead.

🛠️ Real-World Usage Scenarios

Scenario 1: Generating User Profiles for E2E Tests

You need consistent, realistic user objects with names, emails, and addresses.

✅ Best choice: @faker-js/faker
Why? Rich person/address modules, seeding support, and active maintenance.

import { faker } from '@faker-js/faker';
faker.seed(42);
const user = {
  name: faker.person.fullName(),
  email: faker.internet.email(),
  address: faker.location.streetAddress()
};

Scenario 2: Creating Mock API Responses with Custom Formats

Your backend returns IDs like USR-XXXX and order codes like ORD-9A3B.

✅ Best choice: randexp + faker
Why? Use faker for semantic data and randexp for pattern-based IDs.

import RandExp from 'randexp';
import { faker } from '@faker-js/faker';

const userId = new RandExp(/USR-[A-Z0-9]{4}/).gen();
const orderCode = new RandExp(/ORD-[0-9A-Z]{4}/).gen();
const payload = {
  id: userId,
  code: orderCode,
  customer: faker.person.fullName()
};

Scenario 3: Lightweight Test Data in a Browser Environment

You’re writing unit tests in Jest and want minimal dependencies.

✅ Best choice: chance
Why? Small footprint, simple API, and no heavy locale bundles.

import Chance from 'chance';
const chance = new Chance();
test('user creation', () => {
  const mockUser = { name: chance.name(), age: chance.age() };
  // ...
});

Scenario 4: Legacy Codebase Using `casual`

You inherited a project using casual and need to decide whether to migrate.

✅ Recommendation: Plan a migration to @faker-js/faker
Why? casual won’t receive security patches or compatibility updates.

📊 Summary Table

Feature	`casual`	`chance`	`@faker-js/faker`	`randexp`
Active Maintenance	❌ No	⚠️ Maintenance mode	✅ Yes	✅ Yes
Locale Support	❌ Limited	❌ Minimal	✅ Extensive	✅ Via regex patterns
Seeding	✅ Global seed	✅ Per-instance seed	✅ `.seed()` method	❌ Not supported
Extensibility	✅ `define()`	✅ Mixins	✅ Direct assignment	✅ Write new regex
Primary Use Case	Legacy projects	Simple, lightweight	Full-featured mocking	Regex-based strings

💡 Final Recommendation

For new projects, use @faker-js/faker as your primary fake data generator. It’s the most capable, well-maintained, and flexible option.
Reach for randexp when you need to generate strings that match specific formats not covered by semantic generators (e.g., license keys, serial numbers).
Consider chance only if you need a tiny, zero-locale-footprint library for basic randomness in constrained environments.
Avoid casual in new codebases due to lack of maintenance.

Remember: these tools are for development and testing only. Never use them to generate real user data or in production data pipelines.

How to Choose: casual vs chance vs faker vs randexp

casual:
Avoid casual in new projects — it is no longer actively maintained and lacks modern features like robust locale support or security updates. If you encounter it in a legacy codebase, plan a migration to a maintained alternative like @faker-js/faker.
chance:
Choose chance if you need a lightweight, stable library for basic fake data generation in environments where bundle size matters and advanced features like internationalization aren’t required. It’s suitable for simple unit tests or small internal tools, but don’t expect new features or extensive locale coverage.
faker:
Use @faker-js/faker (not the deprecated faker package) for most modern applications. It offers comprehensive, locale-aware data generators, strong seeding support, active maintenance, and a clean, modular API. It’s the best choice for end-to-end testing, UI demos, and any scenario requiring realistic, structured mock data.
randexp:
Pick randexp when you need to generate strings that conform to a specific format defined by a regular expression — such as license keys, tracking IDs, or custom validation patterns. It doesn’t replace semantic data generators but complements them when pattern-based randomness is required.

Popular Comparisons

casual

chance

faker

randexp

README for casual

Fake data generator

Installation

npm install casual

Usage

var casual = require('casual');

// Generate random sentence
// You don't need function call operator here
// because most of generators use properties mechanism
var sentence = casual.sentence;

// Generate random city name
var city = casual.city;

// Define custom generator
casual.define('point', function() {
	return {
		x: Math.random(),
		y: Math.random()
	};
});

// Generate random point
var point = casual.point;

// And so on..

Casual uses javascript properties for common generators so you don't need to use function call operator

Embedded generators


// Address

casual.country              // 'United Kingdom'
casual.city                 // 'New Ortiz chester'
casual.zip(digits = {5, 9}) // '26995-7979' (if no digits specified then random selection between ZIP and ZIP+4)
casual.street               // 'Jadyn Islands'
casual.address              // '6390 Tremblay Pines Suite 784'
casual.address1             // '8417 Veda Circles'
casual.address2             // 'Suite 648'
casual.state                // 'Michigan'
casual.state_abbr           // 'CO'
casual.latitude             // 90.0610
casual.longitude            // 180.0778
casual.building_number      // 2413

// Text

casual.sentence               // 'Laborum eius porro consequatur.'
casual.sentences(n = 3)       // 'Dolorum fuga nobis sit natus consequatur. Laboriosam sapiente. Natus quos ut.'
casual.title                  // 'Systematic nobis'
casual.text                   // 'Nemo tempore natus non accusamus eos placeat nesciunt. et fugit ut odio nisi dolore non ... (long text)'
casual.description            // 'Vel et rerum nostrum quia. Dolorum fuga nobis sit natus consequatur.'
casual.short_description      // 'Qui iste similique iusto.'
casual.string                 // 'saepe quia molestias voluptates et'
casual.word                   // 'voluptatem'
casual.words(n = 7)           // 'sed quis ut beatae id adipisci aut'
casual.array_of_words(n = 7)  // [ 'voluptas', 'atque', 'vitae', 'vel', 'dolor', 'saepe', 'ut' ]
casual.letter                 // 'k'

// Internet

casual.ip           // '21.44.122.149'
casual.domain       // 'darrion.us'
casual.url          // 'germaine.net'
casual.email        // 'Josue.Hessel@claire.us'
casual.user_agent   // 'Mozilla/5.0 (Windows NT 6.1; WOW64; rv:34.0) Gecko/20100101 Firefox/34.0'

// Person

casual.name            // 'Alberto'
casual.username        // 'Darryl'
casual.first_name      // 'Derek'
casual.last_name       // 'Considine'
casual.full_name       // 'Kadin Torphy'
casual.password        // '(205)580-1350Schumm'
casual.name_prefix     // 'Miss'
casual.name_suffix     // 'Jr.'
casual.company_name    // 'Cole, Wuckert and Strosin'
casual.company_suffix  // 'Inc'
casual.catch_phrase    // 'Synchronised optimal concept'
casual.phone           // '982-790-2592'

// Numbers

casual.random                            // 0.7171590146608651 (core generator)
casual.integer(from = -1000, to = 1000)  // 632
casual.double(from = -1000, to = 1000)   // -234.12987444
casual.array_of_digits(n = 7)            // [ 4, 8, 3, 1, 7, 6, 6 ]
casual.array_of_integers(n = 7)          // [ -105, -7, -532, -596, -430, -957, -234 ]
casual.array_of_doubles(n = 7)           // [ -866.3755785673857, -166.62194719538093, ...]
casual.coin_flip                         // true

// Date

casual.unix_time                    // 659897901
casual.moment                       // moment.js object see http://momentjs.com/docs/
casual.date(format = 'YYYY-MM-DD')  // '2001-07-06' (see available formatters http://momentjs.com/docs/#/parsing/string-format/)
casual.time(format = 'HH:mm:ss')    // '03:08:02' (see available formatters http://momentjs.com/docs/#/parsing/string-format/)
casual.century                      // 'IV'
casual.am_pm                        // 'am'
casual.day_of_year                  // 323
casual.day_of_month                 // 9
casual.day_of_week                  // 4
casual.month_number                 // 9
casual.month_name                   // 'March'
casual.year                         // 1990
casual.timezone                     // 'America/Miquelon'

// Payments

casual.card_type            // 'American Express'
casual.card_number(vendor)  // '4716506247152101' (if no vendor specified then random)
casual.card_exp             // '03/04'
casual.card_data            // { type: 'MasterCard', number: '5307558778577046', exp: '04/88', holder_name: 'Jaron Gibson' }

// Misc

casual.country_code    // 'ES'
casual.language_code   // 'ru'
casual.locale          // 'hi_IN'
casual.currency        // { symbol: 'R', name: 'South African Rand', symbol_native: 'R', decimal_digits: 2, rounding: 0, code: 'ZAR', name_plural: 'South African rand' }		
casual.currency_code   // 'TRY'
casual.currency_symbol // 'TL'
casual.currency_name   // Turkish Lira
casual.mime_type       // 'audio/mpeg'
casual.file_extension  // 'rtf'
casual.boolean         // true
casual.uuid            // '2f4dc6ba-bd25-4e66-b369-43a13e0cf150'

// Colors

casual.color_name       // 'DarkOliveGreen'
casual.safe_color_name  // 'maroon'
casual.rgb_hex          // '#2e4e1f'
casual.rgb_array        // [ 194, 193, 166 ]

Define custom generators

casual.define('user', function() {
	return {
		email: casual.email,
		firstname: casual.first_name,
		lastname: casual.last_name,
		password: casual.password
	};
});

// Generate object with randomly generated fields
var user = casual.user;

If you want to pass some params to your generator:

casual.define('profile', function(type) {
	return {
		title: casual.title,
		description: casual.description,
		type: type || 'private'
	};
});

// Generate object with random data
var profile = casual.profile('public');

NOTE: if getter function has non-empty arguments list then generator should be called as function casual.profile('public'), otherwise it should be accessed as property casual.profile.

Localization

You can get localized version of casual generator:

var casual = require('casual').ru_RU;
casual.street; // 'Бухарестская'

Default locale is en_US.

See src/providers/{{locale}} for more details about available locales and locale specific generators.

If you don't find necessary locale, please create an issue or just add it :)

Helpers

random_element

Get random array element

var item = casual.random_element(['ball', 'clock', 'table']);

random_value

Extract random object value

var val = casual.random_value({ a: 1, b: 3, c: 42 });
// val will be equal 1 or 3 or 42

random_key

Extract random object key

var val = casual.random_key({ a: 1, b: 3, c: 42 });
// val will be equal 'a' or 'b' or 'c'

populate

Replace placeholders with generators results

casual.populate('{{email}} {{first_name}}');
// 'Dallin.Konopelski@yahoo.com Lyla'

populate_one_of

Pick random element from given array and populate it

var formats = ['{{first_name}}', '{{last_name}} {{city}}'];
casual.populate_one_of(formats);

// Same as

casual.populate(casual.random_element(formats));

numerify

Replace all # in string with digits

var format = '(##)-00-###-##';
casual.numerify(format); // '(10)-00-843-32'

define

See custom generators

register_provider

var words = ['flexible', 'great', 'ok', 'good'];
var doge_provider = {
	such: function() {
		return 'such ' + casual.random_element(words);
	},

	doge_phrase: function() {
		return 'wow ' + casual.such();
	}
};

casual.register_provider(doge_provider);

casual.such;        // 'such good'
casual.doge_phrase; // 'wow such flexible'

Seeding

If you want to use a specific seed in order to get a repeatable random sequence:

casual.seed(123);

It uses Mersenne Twister pseudorandom number generator in core.

Generators functions

If you want to pass generator as a callback somewhere or just hate properties you always can access generator function at casual._{generator}

// Generate value using function
var title = casual._title();
// Same as
var title = casual.title;

// Pass generator as callback
var array_of = function(times, generator) {
	var result = [];

	for (var i = 0; i < times; ++i) {
		result.push(generator());
	}

	return result;
};

// Will generate array of five random timestamps
var array_of_timestamps = array_of(5, casual._unix_time);

Or you can get functional version of casual generator:

var casual = require('casual').functions();

// Generate title
casual.title();

// Generate timestamp
casual.unix_time();

View providers output cli

There is a simple cli util which could be used to view/debug providers output:

# Will render table with columns [generator_name, result] for all providers
node utils/show.js

 # Will render table with columns [generator_name, result] only for person provider
node utils/show.js person

Browserify support

Currently you can't use casual with browserify. Please check out this browserify-friendly fork Klowner/casual-browserify

Contributing

Adding new locale

License

Heavily inspired by https://github.com/fzaninotto/Faker

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.