bzalasky / tcomb

Type checking and DDD for JavaScript

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; }, 'Integer');  // <= give a name for better debug messages

// 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
}, 'Person'); // <= give a name for better debug messages

// 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 value undefined supplied to Person/age: 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)