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

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

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.

TypeScript / Flowtype users

You may want to check out io-ts

IMPORTANT: Running in production

tcomb is supposed to be used in development and is disabled in production. If you want type checks in production you may use

• tcomb-validation
• io-ts

Setup

npm install tcomb --save

Code example

A type-checked function:

import t from 'tcomb';

function sum(a, b) {
  t.Number(a);
  t.Number(b);
  return a + b;
}

sum(1, 's'); // throws '[tcomb] Invalid value "s" supplied to Number'

// using babel-plugin-tcomb
function sum(a: number, b: number) {
  return a + b;
}

A user defined type:

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

A type-checked class:

const Person = t.struct({
  name: t.String,              // required string
  surname: t.maybe(t.String),  // optional string
  age: t.Integer,                // required integer
  tags: t.list(t.String)       // a list of strings
}, 'Person');

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

const person = Person({
  surname: 'Canti'
}); // throws '[tcomb] Invalid value undefined supplied to Person/name: String'

Chrome DevTools:

Docs

• API
• A little guide to runtime type checking and runtime type introspection (Work in progress)

Features

Lightweight

3KB gzipped, no dependencies.

Type safety

All models defined with tcomb are type-checked.

Note. Instances are not boxed, this means that tcomb works great with lodash, Ramda, etc. And you can of course use them as props to React components.

Based on set theory

• Blog post: JavaScript, Types and Sets - Part I
• Blog post: JavaScript, Types and Sets - Part II

Domain Driven Design

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

• user defined types
• structs
• lists
• enums
• refinements
• unions
• intersections
• the option type
• tuples
• dictionaries
• functions
• recursive and mutually recursive types
• interfaces

Immutability and immutability helpers

Instances are immutable 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:

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

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

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

See Updating immutable instances 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).

Runtime type introspection

All models are inspectable at runtime. You can read and reuse the information stored in your types (in the meta static member). 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 / deserialization

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

• Blog post: JSON Deserialization Into An Object Model

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 for a great DX
};

// .. or define your own behavior
t.fail = function fail(message) {
  console.error(message);
};

Pattern matching

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

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

Babel plugin

Using babel-plugin-tcomb you can also write (Flow compatible) type annotations:

function sum(a: number, b: number): number {
  return a + b;
}

TypeScript definition file

index.d.ts

Contributors

• Giulio Canti maintainer
• Becky Conning func combinator ideas and documentation
• Andrea Lattuada declare combinator

How to Build a standalone bundle

git clone [e-mail]:gcanti/tcomb.git
cd tcomb
npm install
npm run dist

Will output 2 files:

• dist/tcomb.js (development)
• dist/tcomb.min.js (production) Object.freeze calls and asserts stripped out

Related libraries

• tcomb-doc Documentation tool for tcomb
• tcomb-validation Validation library based on type combinators
• tcomb-json-schema Transforms a JSON Schema to a tcomb type
• reactuate React/Redux stack (not a boilerplate kit)
• tcomb-react Alternative syntax for PropTypes
• mongorito-tcomb Bring schema validation to Mongorito thanks to tcomb
• tcomb-form Forms library for react
• tcomb-form-types Adds Types/Validations to tcomb-form
• tcomb-form-native Forms library for react-native
• tcomb-generate Generates random data by tcomb type for property-based testing
• tcomb-additional-types Provides additional predefined types for your existing tcomb setup
• tcomb-builder An immutable syntax for defining tcomb types and forms

Similar projects

• typed-immutable
• immu
• immutable
• mori
• seamless-immutable
• deep-freeze
• freezer
• icedam
• ObjectModel
• rfx

License

The MIT License (MIT)

Changelog

v3.2.29

• Bug Fix
  • [typescript] fix interface's extend signature, #329 (@apepper)