tcomb

What is tcomb?

The tcomb npm package is a library for Node.js and the browser which allows you to check the types of JavaScript values at runtime with a simple and concise syntax. It is useful for enforcing type safety, defining domain models, and creating composable and reusable type checkers.

What are tcomb's main functionalities?

Type Checking

This feature allows you to define a structure with specific types and create instances that adhere to those types.

const t = require('tcomb');
const Person = t.struct({ name: t.String, age: t.Number });
const person = Person({ name: 'Giulio', age: 43 });

Function Argument Validation

This feature enables you to validate function arguments to ensure they are of the expected type.

const t = require('tcomb');
function sum(a, b) {
  t.Number(a);
  t.Number(b);
  return a + b;
}
sum(1, 2);

Subtyping

This feature allows you to create subtypes based on existing types with additional constraints.

const t = require('tcomb');
const Positive = t.subtype(t.Number, n => n >= 0);
const positiveNumber = Positive(10);

Refinement

This feature is similar to subtyping but is specifically for refining types to a more specific subset.

const t = require('tcomb');
const Integer = t.refinement(t.Number, n => n % 1 === 0);
const integerNumber = Integer(42);

Enums

This feature allows you to define a set of constants and ensure values match one of those constants.

const t = require('tcomb');
const Role = t.enums({ Admin: 'Admin', User: 'User' });
const userRole = Role('User');

Other packages similar to tcomb

prop-types

Prop-types is a library for React that is used to document the intended types of properties passed to components. It is similar to tcomb in that it provides runtime type checking, but it is specifically tailored for React's component props.

io-ts

io-ts is a TypeScript runtime type system for IO decoding/encoding. It is similar to tcomb in providing runtime type checking and validation, but it leverages TypeScript's type system for added compile-time safety.

joi

Joi is an object schema description language and validator for JavaScript objects. It provides a powerful and expressive way to define and validate data structures. It is similar to tcomb in terms of validation capabilities but has a different API and is often used for validating API input.

ajv

Ajv is a JSON schema validator. It validates data against JSON Schema standards and is similar to tcomb in terms of validation. However, it uses a JSON-based schema definition rather than a programmatic API.

README

tcomb is a library for Node.js and the browser which allows you to check the types of JavaScript values at runtime with a simple and concise syntax. It's great for Domain Driven Design and for adding safety to your internal code.

"Si vis pacem, para bellum" - (Vegetius 5th century)

Code example

var t = require('tcomb');

// a user defined type
var Integer = t.subtype(t.Number, function (n) => { return n % 1 === 0; });

// a struct
var Person = t.struct({
  name: t.String,              // required string
  surname: t.maybe(t.String),  // optional string
  age: Integer,                // required integer
  tags: t.list(t.String)       // a list of strings
});

// methods are defined as usual
Person.prototype.getFullName = function () {
  return `${this.name} ${this.surname}`;
};

// an instance of Person (the keyword new is optional)
var person = new Person({
  name: 'Giulio',
  surname: 'Canti',
  age: 41,
  tags: ['js developer', 'rock climber']
});

Features

Lightweight

3KB gzipped.

Domain Driven Design

Write complex domain models in a breeze and with a small code footprint. Supported types:

• user defined types
• structs
• lists
• enums
• subtypes
• unions
• intersections
• the option type
• tuples
• dictionaries
• functions

Based on set theory

Blog posts:

• JavaScript, Types and Sets - Part I
• JavaScript, Types and Sets - Part II

Type safety

All models are type checked:

var person = new Person({
  name: 'Giulio',
  // missing required field "age"
  tags: ['js developer', 'rock climber']
});

Output to console:

[tcomb] Invalid argument value = undefined supplied to irreducible type Number

See "Debugging with Chrome DevTools" section for details.

Immutability and immutability helpers

Instances are immutables using Object.freeze. This means you can use standard JavaScript objects and arrays. You don't have to change how you normally code. You can update an immutable instance with the provided update(instance, spec) function:

var person2 = Person.update(person, {
  name: {$set: 'Guido'}
});

where spec is an object contaning commands. The following commands are compatible with the Facebook Immutability Helpers:

• $push
• $unshift
• $splice
• $set
• $apply
• $merge

See Updating immutable instances in the docs for details.

Speed

Object.freeze calls and asserts are executed only in development and stripped out in production (using process.env.NODE_ENV = 'production' tests).

Debugging with Chrome DevTools

You can customize the behavior when an assert fails leveraging the power of Chrome DevTools.

// use the default...
t.fail = function fail(message) {
  throw new TypeError('[tcomb] ' + message); // set "Pause on exceptions" on the "Sources" panel
};

// .. or define your own behavior
t.fail = function fail(message) {
  debugger; // starts the Chrome DevTools debugger
  throw new TypeError(message);
};

Runtime type introspection

All models are inspectable at runtime. You can read and reuse the informations stored in your types (in a meta static property). See The meta object in the docs for details.

Libraries exploiting tcomb's RTI:

• tcomb-validation
• tcomb-form
• Blog post: JSON API Validation In Node.js

Easy JSON serialization / deseralization

Encodes / decodes your domain models to / from JSON for free.

• Blog post: JSON Deserialization Into An Object Model

Pattern matching

// this example uses ES6 syntax

const result = t.match(1,
  t.String, () => 'a string',
  t.Number, () => 'a number'
);

console.log(result); // => 'a number'

Docs

GUIDE.md

Contributors

• Giulio Canti mantainer
• Becky Conning func combinator ideas and documentation.

Similar projects

• immu
• immutable
• mori
• seamless-immutable
• deep-freeze
• freezer
• icedam
• immutable-store

License

The MIT License (MIT)