Synopsis

par is a JavaScript implementation of partial function application (sometimes incorrectly called "currying").

How is this different from Function#bind?

The primary purpose of Function#bind is to create a closure to preserve a function's context (the this variable). Most implementations, including the one in ES 5, also allow partial function application.

The functions provided by par also create closures, but they pass their own context along. This means Function#apply, Function#call and method invocation syntax still behave as expected (with the context being set accordingly).

If you don't care about contexts (e.g. the function you want to wrap doesn't use this), lpartial and Function#bind can be used interchangeably.

There is no native equivalent of rpartial.

Another important distinction is that unlike Function#bind, par works in environments that don't support ECMAScript 5, such as legacy versions of Internet Explorer (versions 8 and lower) or Rhino (e.g. the version bundled with Sun JDK 1.6).

Install

Node.js

With NPM

npm install par

From source

git clone https://github.com/pluma/par.git
cd par
npm install
make && make dist

Browser

With component

component install pluma/par

Learn more about component.

With bower

bower install par

Learn more about bower.

With a CommonJS module loader

Download the latest minified CommonJS release and add it to your project.

Learn more about CommonJS modules.

With an AMD module loader

Download the latest minified AMD release and add it to your project.

Learn more about AMD modules.

As a standalone library

Download the latest minified standalone release and add it to your project.

<script src="/your/js/path/par.globals.min.js"></script>

This makes the par module available in the global namespace.

Basic usage example

var par = require('par');

function divideBy(x, y) {
    return x / y;
}

var divide4By = par(divideBy, 4);
console.log(divide4By(10)); // 0.4

var divideBy4 = par.rpartial(divideBy, 4);
console.log(divideBy4(10)); // 2.5

Wrap-around example

var par = require('par');

function say() {
    // This assumes a modern browser or recent version of IE
    console.log.apply(console, arguments);
}

say('I love Internet Explorer!'); // "I love Internet Explorer!"

var sarcastic = par.rpartial(par(say, '[sarcasm]'), '[/sarcasm]');

sarcastic('I love Internet Explorer!'); // "[sarcasm] I love Internet Explorer! [/sarcasm]"

API

par(fn, args…):Function

Creates a partially applied function that will append the initial arguments to the left-hand side of the argument list.

par.rpartial(fn, args…):Function

Creates a partially applied function that will append the initial arguments to the right-hand side of the argument list.

par.lpartial(fn, args…):Function

Alias for par.

Unlicense

This is free and unencumbered public domain software. For more information, see http://unlicense.org/ or the accompanying UNLICENSE file.