match-operator

Match Operator

This package is an attempt to port the match control structure, which exists in various languages (Rust, Scala, Kotlin, PHP, ...) as a JS function, the closest possible way.

Example:

import match from 'match-operator'

const food = 'strawberry'
const description = match(food, [
  ['apple', 'This food is an apple'],
  ['strawberry', 'raspberry', 'This food is a red fruit'], // First array items are subjects, last one is the result
]) // This food is a red fruit

const food = 'unknown'
const description = match(food, [
  ['apple', 'This food is an apple'],
  ['strawberry', 'raspberry', 'This food is a red fruit'],
]) // UnhandledMatchError

const food = 'unknown'
const description = match(food, [
  ['apple', 'This food is an apple'],
  ['strawberry', 'raspberry', 'This food is a red fruit'],
  [match.default, 'This food is unknown']
]) // This food is unknown

Lazy expressions

You can also use a function to evaluate the result, which will be called only if the subject matches:

const food = 'banana'
const description = match(food, [
  ['apple', () => 'This food is an apple'], // it won't be evaluated because it's a banana
  ['strawberry', () => "This function won't be evaluated"], // same here
  [match.default, (subject) => `We don't know this food, but it looks like ${subject}`],
])

Alternate syntaxes

Array of subjects

You can use an array of subjects if you find it more readable.

const description = match(food, [
  [['strawberry', 'raspberry', 'cherry'], 'This food is a red fruit'],
  [['peach', 'pineapple'], 'This food is a yellow fruit'],
]) 

Object-style rules

You can also use a simple object to define your matching rules, which can be more concise for simple key-value matches:

const fallback = () => 'This food is unknown'
const description = match(food, {
  'apple': 'This food is an apple',
  'strawberry': 'This food is a red fruit'
}, fallback)

This is equivalent to the array syntax and supports all features including function evaluation:

const description = match(food, {
  'apple': (subject) => `This food is an ${subject}`,
  'strawberry': 'This food is a red fruit'
})

Installation

npm install match-operator --save # If you're using NPM
yarn add match-operator # If you're using Yarn

Tests

npm run test # If you're using NPM
yarn test # If you're using Yarn

Disclaimer

This is my first Typescript package - please be kind!

License

MIT.