blakeembrey / arity

Set the length of a function in JavaScript

Arity

Set a functions arity (the argument count) by proxying function calls.

P.S. If you don't care about this and want to receive the exact arity of function arguments, use nary. It uses function invocation (faster!) over .apply to proxy arguments.

Why would I use this?

You probably won't. The reason it needs to exist is for functional utilities and backward compatibility with user expectations. Many modules use function arity to decide how the function should behave (e.g. middleware in express or callbacks in mocha).

Installation

npm install util-arity --save

Usage

var fn = function () {};
var arity = require('util-arity');

var oneArg = arity(1, fn);
var twoArgs = arity(2, fn);
var threeArgs = arity(3, fn);

oneArgs.length; //=> 1
twoArgs.length; //=> 2
threeArgs.length; //=> 3

TypeScript

The typings for this project are available for node module resolution with TypeScript.

License

MIT

arity's Issues

Different approach

I got here via cucumber/cucumber-js#514 and while doing some experiments I came up with a simpler approach, which seems to work for me and wanted to know if you see any issues with this:

const wrappedFn = (...args) => originalFn.apply(this, args);
Object.defineProperty(wrappedFn, 'length', { value: intendedLength });