js-pattern

Tiny javascript library for pattern matching. Inspired by ts-pattern.

Dependencies

None.

Installation

• Using npm: npm i @nerds.sh/js-pattern
• Using yarn: yarn add @nerds.sh/js-pattern

Usage

The library exposes a single function called match.

Use the .with operator to add cases. .with receives two parameters:

• condition -> condition for the match, can be literal, an array of literals, a boolean or a lambda
• lambda -> function to run on match

The .with operator can be chained endlessly.

Use the .like operator for comparing object fields. It can be endlessly chained and combined with the .with operator.

import match from 'js-pattern'

const matchResponse = response => match(response)
    .like({status: 200}, () => console.log('OK'))
    .like({status: 400}, () => console.log('Bad arguments'))
    .like({status: 404}, () => console.log('Not found'))
    .otherwise(() => console.log('Unknown error'))

Use the .has operator for checking for object fields. It can be endlessly chained and combined with the .with and .like operators.

import match from 'js-pattern'

const person = {
    name: 'Mihai',
    job: 'Programmer'
}

const isEmployed = () => match(person)
    .has('job', () => console.log('Employed'))
    .otherwise(() => console.log('Unemployed'))

Use the .otherwise operator to add a default case. It takes a single parameter, lambda, which is the function to be run upon match. Using the .otherwise operator will run the matching.

Use the .execute to run the actual matching.

import match from 'js-pattern'

const sayHiToMihai = name => match(name)
    .with('Mihai Miuta', () => console.log('Hi, my creator'))
    .with(name === 'Mihai Radulescu', () => console.log('Hi, fellow Nerd Mihai'))
    .with(() => name === 'Other Mihai', () => console.log('Hi, fellow Mihai'))
    .otherwise(() => console.log(`Hi, person who's not Mihai`))