Editing Multiple dispatch (section)

==== JavaScript ====
In languages that do not support multiple dispatch at the language definition or syntactic level, it is often possible to add multiple dispatch using a [[Library (computing)|library]] extension. JavaScript and TypeScript do not support multimethods at the syntax level, but it is possible to add multiple dispatch via a library. For example, the ''multimethod package''<ref name="multimethod_package">[https://www.npmjs.com/package/@arrows/multimethod @arrows/multimethod] Multiple dispatch in JavaScript/TypeScript with configurable dispatch resolution by Maciej Cąderek.</ref> provides an implementation of multiple dispatch, generic functions.

Dynamically-typed version in JavaScript:

<syntaxhighlight lang="javascript">
import { multi, method } from '@arrows/multimethod'

class Asteroid {}
class Spaceship {}

const collideWith = multi(
  method([Asteroid, Asteroid], (x, y) => {
    // deal with asteroid hitting asteroid
  }),
  method([Asteroid, Spaceship], (x, y) => {
    // deal with asteroid hitting spaceship
  }),
  method([Spaceship, Asteroid], (x, y) => {
    // deal with spaceship hitting asteroid
  }),
  method([Spaceship, Spaceship], (x, y) => {
    // deal with spaceship hitting spaceship
  }),
)
</syntaxhighlight>

Statically-typed version in TypeScript:

<syntaxhighlight lang="typescript">
import { multi, method, Multi } from '@arrows/multimethod'

class Asteroid {}
class Spaceship {}

type CollideWith = Multi & {
  (x: Asteroid, y: Asteroid): void
  (x: Asteroid, y: Spaceship): void
  (x: Spaceship, y: Asteroid): void
  (x: Spaceship, y: Spaceship): void
}

const collideWith: CollideWith = multi(
  method([Asteroid, Asteroid], (x, y) => {
    // deal with asteroid hitting asteroid
  }),
  method([Asteroid, Spaceship], (x, y) => {
    // deal with asteroid hitting spaceship
  }),
  method([Spaceship, Asteroid], (x, y) => {
    // deal with spaceship hitting asteroid
  }),
  method([Spaceship, Spaceship], (x, y) => {
    // deal with spaceship hitting spaceship
  }),
)
</syntaxhighlight>