1  # universalify
 2  
 3  [![Travis branch](https://img.shields.io/travis/RyanZim/universalify/master.svg)](https://travis-ci.org/RyanZim/universalify)
 4  ![Coveralls github branch](https://img.shields.io/coveralls/github/RyanZim/universalify/master.svg)
 5  ![npm](https://img.shields.io/npm/dm/universalify.svg)
 6  ![npm](https://img.shields.io/npm/l/universalify.svg)
 7  
 8  Make a callback- or promise-based function support both promises and callbacks.
 9  
10  Uses the native promise implementation.
11  
12  ## Installation
13  
14  ```bash
15  npm install universalify
16  ```
17  
18  ## API
19  
20  ### `universalify.fromCallback(fn)`
21  
22  Takes a callback-based function to universalify, and returns the universalified  function.
23  
24  Function must take a callback as the last parameter that will be called with the signature `(error, result)`. `universalify` does not support calling the callback with three or more arguments, and does not ensure that the callback is only called once.
25  
26  ```js
27  function callbackFn (n, cb) {
28    setTimeout(() => cb(null, n), 15)
29  }
30  
31  const fn = universalify.fromCallback(callbackFn)
32  
33  // Works with Promises:
34  fn('Hello World!')
35  .then(result => console.log(result)) // -> Hello World!
36  .catch(error => console.error(error))
37  
38  // Works with Callbacks:
39  fn('Hi!', (error, result) => {
40    if (error) return console.error(error)
41    console.log(result)
42    // -> Hi!
43  })
44  ```
45  
46  ### `universalify.fromPromise(fn)`
47  
48  Takes a promise-based function to universalify, and returns the universalified  function.
49  
50  Function must return a valid JS promise. `universalify` does not ensure that a valid promise is returned.
51  
52  ```js
53  function promiseFn (n) {
54    return new Promise(resolve => {
55      setTimeout(() => resolve(n), 15)
56    })
57  }
58  
59  const fn = universalify.fromPromise(promiseFn)
60  
61  // Works with Promises:
62  fn('Hello World!')
63  .then(result => console.log(result)) // -> Hello World!
64  .catch(error => console.error(error))
65  
66  // Works with Callbacks:
67  fn('Hi!', (error, result) => {
68    if (error) return console.error(error)
69    console.log(result)
70    // -> Hi!
71  })
72  ```
73  
74  ## License
75  
76  MIT