Powerful and lightweight deep pattern matching for Javascript

pnmg

Pattern matching consists of specifying patterns to which some data should conform and then checking to see if it does. Way to select behaviors based on the structure of a value in a similar way to destructuring.

The pnmg provides deep matching functionality with usefull extra types. Leads to write functional, immutable and expressive code.

switch with ~~blackja...~~ declarative style and deep matching.

Installation

NPM

npm install --save pnmg

Patterns

Object Patterns

Object patterns match objects with certain properties. Additional properties may be present on the matched object. Examples:

import {match} from 'pnmg';

const arg = {/* data */};

match(arg)
  .when({}, () => {/* Match empty object */})
  .when({users: Array}, ({users}) => users.map(user => user.id))
  .when({x: 42, y: String}, obj => {/* Match object where x is 42 and y is String */})
  .when(Object, () => {/* Match any object */})
  .default(notObj => {/* default handler if none of patterns confirmed */});

Array Patterns

Examples:

import {match, Guard} from 'pnmg';

match(arg)
  .when([], () => {/* match an empty array */})
  .when([true, false], () => 'First el is true, second is false')
  .when([{WUF: 'WUFF'}], () => 'First element is Object with WUF attr with WUFF value')
  .when(Guard(arr => arr.length > 4), () => 'Array length greater than 4')
  .when(Array, ([head, ...tail]) => `Head is ${head} and tails is ${tail}`)
  .default(notArray => `${notArray} not Array`);

Literal Patterns

Literal patterns are string, number, boolean, null, and undefined literals and matches exactly that value. Examples:

match(arg)
  .when('WUF', str => {/* match the String value "WUF" */})
  .when(42, () => {/* match the Number value 42 */})
  .when(true, () => {/* match true */})
  .when(Boolean, () => {/* match any Boolean */})
  .default(() => `${arg} not matched`);

Nested Patterns

Patterns can nest. Example:

const isCool = data => match(data)
  .when({info: {cool: true}}, handleCoolData)
  .default(() => 'Not cool');

Types

Defined

You can use Defined if you need to match data that could have any value except undefined.

Guard

Use Guard when value need to match certain condition.

Example:

import {match, Defined, Guard} from 'pnmg';

match(data)
  .when({pos: Guard(x => x > 0)}, arr => {/* Object with 'pos' attr and value > 0 */})
  .when([Defined, 42, Defined], arr => {/* array with at least 3 elements and the second is 42 */})
  .default(() => {/* not match */});
}