Ex Patterns
This project brings Elixir-style pattern matching and control flow structures to JavaScript. Pattern matching is supported for native JavaScript data types as well as common Immutable.js collections. See the documentation for details and examples.
Setup
Install the package from npm:
npm i ex-patterns
Quick Start Guide
match
Function
The A pattern matching function for flat and nested data structures, including
arrays, objects and Immutable.js
collections:
import { match, _, $, A } from 'ex-patterns';
> match([_, 2], [1, 2])
[true, { }]
> match([A, 2], [1, 2])
[true, { A: 1 }]
> match([$('first'), $('second')], [1, 2])
[true, { first: 1, second: 2 }]
when
Function
The A switch statement based on pattern matching, similar to Elixir's case
control flow structure. It accepts any number of match
clauses in the format (pattern, callback)
that are matched against a value.
import { when, end, _, A, H, N } from 'ex-patterns';
const sayHi = (user) => when(user)
({ name: N }, ({ N }) => `Hi ${N}!`)
({ alias: A }, ({ A }) => `Hi ${A}!`)
({ handle: H }, ({ H }) => `Hi ${H}!`)
(_, () => 'Hi!')
(end);
const user = { name: 'Amelie', hometown: 'Stockholm' };
> sayHi(user);
'Hi Amelie!'
suppose
Function
The A control flow structure to leverage the power of pattern matching while
coding for the happy path, similar to Elixir's with
. Takes any number of
clauses in the format (pattern, function)
and checks if the return value of
function
matches pattern
. Matches are piped through the suppose
clauses
until the then
callback is reached. Can be combined with an optional otherwise
clause.
import { suppose, then, otherwise, end, I, N, R } from 'ex-patterns';
const response = await ...
suppose
({ status: 200 }, () => response)
({ body: { name: N, id: I }}, () => response)
(true, ({ I }) => isUniqueUserId(I))
(then)
(({ N }) => `Welcome ${N}`)
(end);
cond
Function
The A compact switch statement that accepts any number of clauses in the format
(truthy?, value)
, similar to Elixir's cond
control flow structure:
import { cond, end } from 'ex-patterns';
const fizzBuzz = (number) => cond
(number % 15 === 0, 'fizzbuzz')
(number % 3 === 0, 'fizz')
(number % 5 === 0, 'buzz')
(true, number)
(end);
> fizzBuzz(5)
'buzz'
Want to learn more?
Head over to the documentation for a lot more details and examples!