js-pattern-match

Implement pattern match in JS.

Install:

Node

babel-runtime is required, or you can consider this way: simple .

// npm i js-pattern-match --save-dev
import match from 'js-pattern-match';

Browser

Since some runtimes joined in, the size of match.min.js is larger than actual. So if you are working with babel, consider this way: Node .

<script src="https://zhengxiaoyao0716.github.io/js-pattern-match/dist/match.min.js"></script>

Simple

If you are using ES6 and working with mordern browser, you can just simple to add those code and it will works well:

const match = ((isArr, isFn, any, mPns) => (mFns => mFns([[[isArr], mFns], [[isArr, isFn], mFns], [[any, isArr], mPns]]))(
    (fns, elseFn) => (...args) => (
        fns.find(([pattern]) => mPns(pattern, args)) || [, elseFn || ((...args) => { throw new Error('no matched pattern.'); })]
    )[1](...args)
))(arr => arr instanceof Array, fn => fn instanceof Function, () => true,
    (pattern, args) => pattern instanceof Function ?
        pattern(...args) : pattern.length == args.length && pattern.every((p, i) => p instanceof Function ? p(args[i]) : p === args[i]));

But, if you need lower browser support, you need to transform those code and make a polyfill for fns.find. For example, using babel with transform-runtime and replace fns.find( with Array.find(fns, .

Usage:

Define a pattern-matched function to handle some values like a response of HTTP request, It will looks like those codes in elixir:

handleResp = fn
    200, result -> "ok, " <> result
    code, result -> "#{code}, #{result}"
end

const any = () => true;
const matchResp = match([
    [[200, any], console.log],
    [[any, any], console.warn],
], console.error);
matchResp(200, 'fin.');
matchResp(404, 'not found.');
matchResp('unexpected.');

Implement the example tc39 given:

// let getLength = vector => match (vector) {
//     { x, y, z }: Math.sqrt(x ** 2 + y ** 2 + z ** 2),
//     { x, y }:    Math.sqrt(x ** 2 + y ** 2),
//     [...]:       vector.length,
//     else: {
//         throw new Error("Unknown vector type");
//     }
// }
const num = Number.isInteger;
const res = (...args) => args.length > 1;
const els = (..._) => true;
let getLength = match([
    [[num, num, num],   (x, y, z) => Math.sqrt(x ** 2 + y ** 2 + z ** 2)],
    [[num, num],        (x, y) => Math.sqrt(x ** 2 + y ** 2)],
    [res,               (...vector) => vector.length],
    [els, (...args) => { throw new Error("Unknown vector type: " + String(args)); }]
]);

It looks alike, and if we have some macro or syntactic sugar we can easier to implements it. See match_test.es6 for more details usage.