rustmatchjs

Rust match is cool. I wish it were in js.

This package provides a set of functions to replicate the Rust language's match expression. Unlike the switch statement in Javascript, match is an expression, which makes it perfect for conditionally assigning one value based on another in a readable way.

The first matching arm will be executed and its value returned. For match.val arms, a shallow comparison is performed to allow matching on objects. Thanks to some magic from Typescript, this can come kinda close to Rust match. The input type, I, will be inferred from the first argument and the output type, O, will be inferred from the type or return type of the first arm's res arg. Finally, a default arm must be included as the last argument. Since Typescript can't make sure your branches are exhaustive, this ensures some value is always returned.

Installation:

# yarn
yarn add rustmatchjs 
# npm
npm i rustmatchjs 

Usage:

const message = match(response,
    match.val({ ...response, code: 200, error: null }, 'Fetched successfully!'),
    match.val({ ...response, code: 404 }, () => {
        console.log('Not found');
        return '404 :0';
    }),
    match.fn(response => response.code >= 500 && response.code < 600, () => {
        console.log(`Server error ${response.code}. Err: ${response.error}`);
        return 'Not your fault friend';
    }),
    match.fn(response => response.error !== null, response.error),
    match.default('I do not know how to handle this'),
    // alias for match.default
    match._(() => 'I do not know how to handle this')
);