mix-classes

Easily add typescript-safe mixins to JS classes, with support for generics, constructors, overloading and more. Correctly handles this for each class, so it'll work with anything.

• Typescript generics
• Pass arguments to mixins, by providing an array of arguments
• Supports super calls in overloaded methods
• Use instanceof to check for mixin classes
• Handles the this inside classes, so that they always access their local scope first. No need to worry about name-collisions

import { Mix } from 'mix-classes'

class Contactable {
  constructor(public email: string, public phone?: string) {}
}
class Nameable {
  constructor(public name: string) {}
}
class Website {
  constructor(public websiteUrl: string) {}
}

class Developer extends Mix(Nameable, Contactable, Website) {
  constructor() {
    super(['Bob'], ['[e-mail]'], ['https://example.com'])
  }
}

class Company extends Mix(Nameable, Contactable) {
  constructor() {
    super(['Apple'], ['[e-mail]', '18-00'], ['https://apple.com'])
  }
}

const developer = new Developer()
developer.name
developer.email
developer.websiteUrl

const company = new Company()
company.name
company.email
company.phone
company.websiteUrl

Constructor arguments

You can pass custom constructor arguments to each mixin within an array inside the super call. The arguments order is dependant on the mix array order.

import { Mix } from 'mix-classes'

class Nameable {
  constructor(public name: string) {}
}

class Ageable {
  constructor(public age: number) {}
}

class Person extends Mix(Nameable, Ageable) {
  constructor() {
    super(['Bob'], [50])
    //     ^ name argument for Nameable
    //              ^ age argument for Ageable
  }
}

Overloading

All mixins are seperate classes with different this values, meaning you don't need to worry about name collisions.

import { Mix, getMixin } from 'mix-classes'

class A {
  variable = 'a'
  public a() {
    return this.variable
  }
}

class B {
  variable = 'b'
  public b() {
    return this.variable
  }
}

class Test extends Mix(A, B) {
  constructor() {
    super()

    // The default value is the last mixin specified
    console.log(this.variable) // 'b'

    // Use getMixin to get overloaded properties
    console.log(getMixin(this, A).variable) // 'a'

    // Mixins retain access to their local variables
    this.a() // 'a'
    this.b() // 'b'
  }
}

const test = new Test()

Typescript generics

Typescript generics are supported, but it requires using Typescript's declaration merging.

To use them, simply wrap the class that you want to pass generics to in Generic(), and then add an interface with the same name as the class you want it in.

Before:

import { Mix } from 'mix-classes'

class MyClass<T extends string = 'initial'> extends Mix(
  User,
  Nameable,
  Ageable
) {}

After:

import { Generic, Mix } from 'mix-classes'

// Move all generic type signatures to the interface
// including default values.
interface MyClass<T extends string = 'initial'> extends User<'bob'> {}

class MyClass<T> extends Mix(Generic(User), Nameable, Ageable) {}

import { Mix, Generic } from 'mix-classes'

class B {}

class Role<Type extends string> {
  constructor(public type: Type) {}
}

class User<Username extends string> {
  constructor(public username: Username) {}
}

interface Admin extends User<'bob'>, Role<'admin'> {}

class Admin extends Mix(Generic(User), Generic(Role), B) {
  constructor() {
    super(['bob'], ['admin'])
  }
}

const test = new Admin()
test.username // type 'bob'