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
import t from 'tcomb';
// a user defined type
const Integer = t.subtype(t.Number, (n) => n % 1 === 0);
// a struct
const 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} ${this.surname}`;
};
// an instance of Person (the keyword new is optional)
const person = new Person({
name: 'Giulio',
surname: 'Canti',
age: 41,
tags: ['js developer', 'rock climber']
});
Features
Lightweight
3KB gzipped.
Domain Driven Design
Write complex domain models in a breeze and with a small code footprint. Supported types:
- user defined types
- structs
- lists
- enums
- subtypes
- unions
- intersections
- the option type
- tuples
- dictionaries
- functions
Based on set theory
Blog posts:
Type safety
All models are type checked:
const person = new Person({
name: 'Giulio',
// missing required field "age"
tags: ['js developer', 'rock climber']
});
Output to console:
[tcomb] Invalid argument value = undefined supplied to irreducible type Number
See "Debugging with Chrome DevTools" section for details.
Immutability and immutability helpers
Instances are immutables using Object.freeze
. This means you can use standard JavaScript objects and arrays. You don't have to change how you normally code. You can update an immutable instance with the provided update(instance, spec)
function:
const person2 = Person.update(person, {
name: {$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:
Easy JSON serialization / deseralization
Encodes / decodes your domain models to / from JSON for free.
- Blog post: JSON Deserialization Into An Object Model
Docs
Contributors
- Giulio Canti mantainer
- Becky Conning
func
combinator ideas and documentation.
License
The MIT License (MIT)