case-match

case-match

JavaScript case matching utility. With TypeScript support.

Usage

The match function takes a value, and a list of cases, and returns either the first case that matches, or an exception otherwise.

import match from 'case-match';

const type = 'foo';
const result = match(type, {
    foo: 42,
    bar: 43,
    baz: 44,
});
result === 42;

A case result can be either a plain value, or a function:

const fruit = 'orange';
const result = match(fruit, {
    apple: 'Apple Pie',
    orange: () => 'Orange Juice',
});
result === 'Orange Juice';

A default case can be specified as fallback. A special symbol match.default is available to use as the key for the default case.

const fruit = 'pear';
const result = match(fruit, {
    apple: 'Apple Pie',
    orange: 'Orange Juice',
    [match.default]: fruit => processOther(fruit),
});

If no case matches, and no fallback is given, an exception is thrown.

Custom match semantics

You can create your own custom match function. For example, let's say we have a React application that makes use of actions that conform to the Flux Standard Action (FSA) protocol. We could create a matcher as follows:

import { matcher } from 'case-match';

const match = matcher(subject => ({
    discriminator: subject.type,
    body: subject,
}));

const action = { type: 'CREATE_USER', error: false, payload: { name: 'John' } };
const result = match(action, {
    CREATE_USER: ({ error, payload }) => doSomethingWith(payload),
});

We supply a couple of common matchers out of the box:

• match: generic matcher
• matchType: match on objects with a type property
• matchSingleKey: match on objects with a single property, e.g. { MY_TYPE: { value: 42 } }

import { matchType, matchSingleKey } from 'case-match';

const action = { type: 'CREATE_USER', error: false, payload: { name: 'John' } };
matchType(action, {
    CREATE_USER: ({ error, payload }) => doSomethingWith(payload),
});

matchSingleKey({ CREATE_USER: { name: 'John' } }, {
    CREATE_USER: user => doSomethingWith(user),
});

Similar libraries

• https://github.com/gvergnaud/ts-pattern
• https://github.com/LestaD/match.js
• https://github.com/eddieantonio/single-key
• https://github.com/FGRibreau/match-when