Merge pull request #64 from DanielRamosAcosta/add-promisify-snippet

Add promisify snippet

README.md

@@ -46,6 +46,7 @@
 * [Percentile](#percentile)
 * [Pipe](#pipe)
 * [Powerset](#powerset)
+* [Promisify](#promisify)
 * [Random integer in range](#random-integer-in-range)
 * [Random number in range](#random-number-in-range)
 * [Randomize order of array](#randomize-order-of-array)
@@ -461,6 +462,24 @@ const powerset = arr =>
 // powerset([1,2]) -> [[], [1], [2], [2,1]]
 ```
 
+### Promisify
+
+Creates a promisified version of the given callback-style function. In Node 8+, you
+can use [`util.promisify`](https://nodejs.org/api/util.html#util_util_promisify_original)
+
+```js
+const promisify = func =>
+  (...args) =>
+    new Promise((resolve, reject) =>
+      func(...args, (err, result) =>
+        err
+        ? reject(err)
+        : resolve(result))
+    )
+// const stat = promisify(fs.stat)
+// stat('foo.txt') -> Promise resolves if `foo.txt` exists, otherwise rejects
+```
+
 ### Random integer in range
 
 Use `Math.random()` to generate a random number and map it to the desired range, using `Math.floor()` to make it an integer.

snippets/promisify.md

@@ -0,0 +1,17 @@
+### Promisify
+
+Use currying to return a function returning a `Promise` that calls the original function. 
+Use the `...rest` operator to pass in all the parameters. 
+
+*In Node 8+, you can use [`util.promisify`](https://nodejs.org/api/util.html#util_util_promisify_original)*
+
+```js
+const promisify = func =>
+  (...args) =>
+    new Promise((resolve, reject) =>
+      func(...args, (err, result) =>
+        err ? reject(err) : resolve(result))
+    );
+// const delay = promisify((d, cb) => setTimeout(cb, d))
+// delay(2000).then(() => console.log('Hi!')) -> Promise resolves after 2s
+```