Match values

Apply pattern matching in JavaScript

Getting started

$ npm install match-values

Usage

• Syntax: match(variable, pattern)
• It can match values and conditions
• Use _ for the default case (Must be the last branch of a pattern)

Match a pattern to get a primitive value

import match from 'match-values'

const pattern = {
  h1: 20,
  h2: 18,
  title: 16,
  description: 14,
  _: 13
}
match('h1', pattern) // 20
match('h2', pattern) // 18
match('title', pattern) // 16
match('description', pattern) // 14
match('anything', pattern) // 13

Match a pattern to get a function

import match from 'match-values'

const handleError = match(error, {
  NOT_FOUND: () => showErrorMessage('Page not found'),
  TIMEOUT: () => showErrorMessage('Page has timed out'),
  _: NOOP
})
handleError()

Advanced Usage

Match a pattern lazily (useful for function composition)

import { lazyMatch } from 'match-values'

const pattern = {
  h1: 20,
  h2: 18,
  title: 16,
  description: 14,
  _: 13
}

const fontSizes = ['h1', 'h2', 'x'].map(lazyMatch(pattern)) // [20, 18, 13]
const getFinalFontSize = compose(
  (size) => size + 1,
  lazyMatch(pattern),
  (font) => font.size
)({
  size: 'description'
}) // 15

Match conditions

const pattern = {
  [x => x > 5, 'smaller'],
  [x => x === 5, 'correct'],
  [_, 'greater']
}
match(8, pattern) // smaller
match(5, pattern) // correct
match(1, pattern) // greater

Licensing

MIT