# JS Promisify

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## Introduction

JS Promisify is a [npm](http://npmjs.org) minimal and well-tested async module for [NodeJS](http://nodejs.org/), that **converts NodeJS async style functions to [native JS promises](http://www.html5rocks.com/en/tutorials/es6/promises/)** (if they're supported by the underlying JavaScript engine, like in Node >= 4.0.0).

For example, it can be used to convert the NodeJS native [file system library](https://nodejs.org/api/fs.html) (`fs`), to easily perform file operations with promises.

## Install

`npm install js-promisify`

(add "--save" if you want the module to be automatically added to your project's "package.json" dependencies)


## Usage

```js
promisify(fun, args, [ctx])
```

- `fun` can be any function with a callback argument that follows the Node JS async function pattern signature (i.e. the callback is the last argument and has a signature `function(err, data)`).
- `args` is an array containing all the arguments that need to be passed to `fun`, excluding the callback.
- `ctx` (optional) is what the variable `this` should be bound to when `fun` is called with the arguments provided through the `args` array.

##### Example
```js
const promisify = require('js-promisify');
const fs = require('fs');

promisify(fs.readFile, ['path/to/myfile.txt', {encoding: 'utf8'}])
  .then(function (data) {
    console.log(data);
  })
  .catch(function (err) {
    console.log(err);
  })

// Same as above, using async / await

(async () => {
  console.log(await promisify(fs.readFile, ['path/to/myfile.txt', {encoding: 'utf8'}]))
})()
```

***

MIT License