Babel-plugin-holes NPM

babel-plugin-holes

This plugin is made to bring the powerful expressivity of Scala functions to JavaScript. It provides a powerful system of holes to help on functional programming and function composition, enforcing the point-free style.

It's very well tested and has consistent rules that shouldn't break when used with other plugins. You can also abstract the native JavaScript operations with it without overheads!

Examples

// Binary operators
const add = _ + _
const increment = _ + 1

console.log(add(100, 200)) // 300
console.log(increment(1000)) // 1001


// Unary operators
const negate = -_

console.log(negate(10)) // -10


// Operators as functions
const at = _[_]
const call = _(_)

console.log(at([5, 10, 15], 1)) // 10
call(console.log, 'Hello!') // 'Hello!'


// Identity function
const id = _

console.log(id('frobnicate')) // 'frobnicate'


// Method calls
const toString = _.toString()
const toHexString = _.toString(16)

console.log(toString(10)) // 10
console.log(toHexString(10)) // 'a'


// Binary property access
const goodPassword = _.length >= 8
const ageSum = _.age + _.age

console.log(goodPassword('dolphins')) // true
console.log(ageSum({ age: 21 }, { age: 30 })) // 51


// Binary method call
const ellipsize = _.toString() + '...'

console.log(ellipsize(100)) // 100...

It works on identifiers, simple members, computed members, calls, binary and unary expressions, so you can compose functions that take more parameters, for example:

const assocOne = assoc(_, 1, _)

console.log(assocOne('value', {})) // { value: 1 }

Disabling in current scope

If you want to use the original underscore, you can disable this plugin in current scope (and its children scopes) using 'no holes' directive.

Options

You can pass your own curry function with { curry: 'curry' }. The generated functions will use it, so:

{
    "plugins": ["holes", { "curry": "curry" }]
}

const add = _ + _

will emit:

const add = curry((_2, _3) => _2 + _3)

Installation

$ npm install --save-dev babel-plugin-holes

Usage

Via `.babelrc` (Recommended)

.babelrc

{
  "plugins": ["holes"]
}

Via CLI

$ babel --plugins holes script.js

Via Node API

require('babel-core').transform('code', {
  plugins: ['holes']
});

Observation

Using ++ and -- has no warranties because Babel code generator has a bug that emits wrong code for a correct AST node. Their use is not recommended.