Lodash Patterns

Mini pattern matching tool leveraging lodash methods. Written in typescript

Installation

Note: Lodash is not included in the module, and has to be installed separately

npm install --save lodash-patterns lodash

Usage

Base usage

import { when, matcher } from 'lodash-patterns'

const detectErrorType = matcher(
  [when("has", "body.errors"), () => "ApiError"],
  [when("isString"), () => "ServerError"],
  [when("isMatch", { message: 'unknown' }), () => "UnknownError"],
  () => "Internal Error" // fallback
)

const errorType = detectErrorType({ message: 'unknown' })

Negative matchers

when.not(...)

import { matcher, when } from '../index'

const isRecordValid = matcher(
  [when.not('isObject'),        () => false],
  [when.not('has', 'username'), () => false],
  () => true
)

Language helpers

otherwise(resolver)

import { when, matcher, otherwise } from 'lodash-patterns'

const detectErrorType = matcher(
  [when("has", "body.errors"), () => "ApiError"],
  otherwise(() => "Unknown Error")
)

const errorType = detectErrorType("oh no")

use(value)

Creates a function that returns the value specified

import { when, matcher, otherwise, use } from 'lodash-patterns'

const movieOf = matcher(
  [when("isEqual", "john travolta"), use("pulp fiction")],
  [when("isEqual", "tom hanks"), use("the terminal")],
  [when("isEqual", "morgan freeman"), use("shawshank")],
  otherwise(use('no movie found'))
)

const movie = movieOf("tom hanks")

Available aliases:

• value(value)

good and bad

Simple functions that return respectively true and false

import { matcher, when, otherwise, bad, good } from '../index'

const isRecordValid = matcher(
  [when.not('isObject'),        bad],
  [when.not('has', 'username'), bad],
  [when.not('has', 'email'),    bad],
  [when('thru', (record) => (<any>record).username.length < 8), bad],
  otherwise(good)
)

isRecordValid({ username: 'jeffgoldblum', email: '[e-mail]'}) // true

Available aliases:

• yes
• no

More examples

Command Runner

import { when, matcher, otherwise } from 'lodash-patterns'

const exec = matcher(
  [when("eq", "commit"),  ()    => fetch('/commit')],
  [when("isString"),      (act) => fetch(`/action/${act}`)]
  [when("isArray"),       (arr) => Promise.all(arr.map(exec))],
  otherwise(
    () => throw 'invalid command'
  )
)

await exec('commit')
await exec(['commit', 'doX', 'doY'])
await exec(1) // throws

React

import _ from 'lodash'
import { when, matcher, use, otherwie } from 'lodash-patterns'

function Component({ data }) {
  const schema = { movies: _.isArray }

  const show = matcher(
    [when('isArray'), (arr) => (
      <div>{ arr.map(show) }</div>
    )],
    [when.not("isObject", use(
      <div> Invalid Data </div>
    )],
    [when.not('conformsTo', schema), use(
      <div>Invalid Schema</div>
    )],
    otherwise(use(
      <ul>
        { data.movies.map(...) }
      </ul>
    )
  )

  return show(data);
}

Development

Install dependencies

npm install

Running tests

npm run test