thenify

Promisify a callback-based function using any-promise.

• Preserves function names
• Uses a native promise implementation if available and tries to fall back to a promise implementation such as bluebird
• Converts multiple arguments from the callback into an Array, also support change the behavior by options.multiArgs
• Resulting function never deoptimizes
• Supports both callback and promise style

An added benefit is that thrown errors in that async function will be caught by the promise!

API

fn = thenify(fn, options)

Promisifies a function.

Options

options are optional.

• options.withCallback - support both callback and promise style, default to false.
• options.multiArgs - change the behavior when callback have multiple arguments. default to true.
• true - converts multiple arguments to an array
• false- always use the first argument

• Array - converts multiple arguments to an object with keys provided in options.multiArgs

• Turn async functions into promises

```js var thenify = require('thenify');

var somethingAsync = thenify(function somethingAsync(a, b, c, callback) { callback(null, a, b, c); }); ```

• Backward compatible with callback

```js var thenify = require('thenify');

var somethingAsync = thenify(function somethingAsync(a, b, c, callback) { callback(null, a, b, c); }, { withCallback: true });

// somethingAsync(a, b, c).then(onFulfilled).catch(onRejected); // somethingAsync(a, b, c, function () {}); ```

or use thenify.withCallback()

```js var thenify = require('thenify').withCallback;

var somethingAsync = thenify(function somethingAsync(a, b, c, callback) { callback(null, a, b, c); });

// somethingAsync(a, b, c).then(onFulfilled).catch(onRejected); // somethingAsync(a, b, c, function () {}); ```

• Always return the first argument in callback

```js var thenify = require('thenify');

var promise = thenify(function (callback) { callback(null, 1, 2, 3); }, { multiArgs: false });

// promise().then(function onFulfilled(value) { // assert.equal(value, 1); // }); ```

• Converts callback arguments to an object

```js var thenify = require('thenify');

var promise = thenify(function (callback) { callback(null, 1, 2, 3); }, { multiArgs: [ 'one', 'tow', 'three' ] });

// promise().then(function onFulfilled(value) { // assert.deepEqual(value, { // one: 1, // tow: 2, // three: 3 // }); // }); ```