tiny-types

Tiny Types

TinyTypes is an npm module that makes it easy for TypeScript and JavaScript projects to give domain meaning to primitive types. It also helps to avoid all sorts of bugs and makes your code easier to refactor.

Installation

To install the module from npm:

npm install --save tiny-types

Defining Tiny Types

An int on its own is just a scalar with no meaning. With an object, even a small one, you are giving both the compiler and the programmer additional information about what the value is and why it is being used.

‐ Jeff Bay, Object Calisthenics

Single-value types

To define a single-value TinyType - extend from TinyTypeOf<T>():

import { TinyTypeOf } from 'tiny-types';

class FirstName extends TinyTypeOf<string>() {}
class LastName  extends TinyTypeOf<string>() {}
class Age       extends TinyTypeOf<number>() {}

Every tiny type defined this way has a readonly property value of type T, which you can use to access the wrapped primitive value. For example:

const firstName = new FirstName('Jan');

firstName.value === 'Jan';

It also has an equals method, which you can use to compare tiny types by value:

const 
    name1 = new FirstName('Jan'),
    name2 = new FirstName('Jan');

name1.equals(name2) === true; 

An additional feature of tiny types is a built-in toString() method (which you can override if you want to, of course):

const name = new FirstName('Jan');

name.toString() === 'FirstName(value=Jan)';

Multi-value and complex types

If the tiny type you want to model has more than one value, or you want to perform additional operations in the constructor, extend from TinyType directly:

import { TinyType } from 'tiny-types';

class Person extends TinyType {
    constructor(public readonly firstName: FirstName,
                public readonly lastName: LastName,
    ) {
        super();
    }
}

You can also mix and match both of the above definition styles:

import { TinyType, TinyTypeOf } from 'tiny-types';

class UserName extends TinyTypeOf<string>() {}

class Timestamp extends TinyTypeOf<Date>() {}

abstract class DomainEvent extends TinyTypeOf<Timestamp>() {}

class AccountCreated extends DomainEvent {
    constructor(public readonly username: UserName, timestamp: Timestamp) {
        super(timestamp);
    }
}

const event = new AccountCreated(new UserName('jan-molak'), new Timestamp(new Date()));

Even such complex types still have both the equals and toString methods:

const 
    now = new Date(2018, 2, 12, 0, 30),
    event1 = new AccountCreated(new UserName('jan-molak'), new Timestamp(now)),
    event2 = new AccountCreated(new UserName('jan-molak'), new Timestamp(now));
    
event1.equals(event2) === true;

event1.toString() === 'AccountCreated(username=UserName(value=jan-molak), value=Timestamp(value=Mon Mar 12 2018 00:30:00 GMT+0000 (GMT)))'

Your feedback matters!

Do you find TinyTypes useful? Give it a star! ★

Found a bug? Need a feature? Raise an issue or submit a pull request.

Have feedback? Let me know on twitter: @JanMolak

License

TinyTypes library is licensed under the Apache-2.0 license.

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- Copyright © 2018- Jan Molak