53 lines
1.7 KiB
Markdown
53 lines
1.7 KiB
Markdown
# Arity
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[![NPM version][npm-image]][npm-url]
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[![NPM downloads][downloads-image]][downloads-url]
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[![Build status][travis-image]][travis-url]
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[![Test coverage][coveralls-image]][coveralls-url]
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> Set a functions arity (the argument count) by proxying function calls.
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**P.S.** If you need need to enforce arity and don't care about argument length or `this`, use [`nary`](https://github.com/blakeembrey/nary). It's magnitudes faster than using `.apply` to proxy arguments.
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## When would I use this?
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It's unlikely you'll need to use this utility in everyday development. The reason I wrote it was for functional utilities and backward compatibility with user expectations. For example, many modules use function arity to decide how the function behaves (e.g. error middleware in `express`, callbacks in `mocha`).
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## Installation
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```
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npm install util-arity --save
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```
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## Usage
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```javascript
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var fn = function () {};
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var arity = require('util-arity');
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var oneArg = arity(1, fn);
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var twoArgs = arity(2, fn);
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var threeArgs = arity(3, fn);
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oneArgs.length; //=> 1
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twoArgs.length; //=> 2
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threeArgs.length; //=> 3
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```
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## TypeScript
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The typings for this project are available for node module resolution with TypeScript.
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## License
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MIT
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[npm-image]: https://img.shields.io/npm/v/util-arity.svg?style=flat
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[npm-url]: https://npmjs.org/package/util-arity
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[downloads-image]: https://img.shields.io/npm/dm/util-arity.svg?style=flat
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[downloads-url]: https://npmjs.org/package/util-arity
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[travis-image]: https://img.shields.io/travis/blakeembrey/arity.svg?style=flat
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[travis-url]: https://travis-ci.org/blakeembrey/arity
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[coveralls-image]: https://img.shields.io/coveralls/blakeembrey/arity.svg?style=flat
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[coveralls-url]: https://coveralls.io/r/blakeembrey/arity?branch=master
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