Support for async/await (#51)

* First draft support for async/await

* Fixed tests using babel

* Re-enabled all tests

* Updated documentation

* wqFixes after review

* Version bump

.babelrc

@@ -0,0 +1,9 @@
+{
+  "presets": [
+    ["env", {
+      "targets": {
+        "node": "6.10"
+      }
+    }]
+  ]
+}

README.md

@@ -23,16 +23,18 @@
   <a href="https://standardjs.com/">
     <img src="https://img.shields.io/badge/code_style-standard-brightgreen.svg" alt="Standard Code Style"  style="max-width:100%;">
   </a>
-  <a href="https://gitter.im/middyjs">
-    <img src="https://badges.gitter.im/gitterHQ/gitter.svg" alt="Chat on Gitter"  style="max-width:100%;">
-  </a>
   <a href="https://greenkeeper.io/">
     <img src="https://badges.greenkeeper.io/middyjs/middy.svg" alt="Greenkeeper badge"  style="max-width:100%;">
   </a>
+  <a href="https://gitter.im/middyjs">
+    <img src="https://badges.gitter.im/gitterHQ/gitter.svg" alt="Chat on Gitter"  style="max-width:100%;">
+  </a>
 </p>
 </div>
 
+
 ## TOC
+
  - [A little appetizer](#a-little-appetizer)
  - [Install](#install)
  - [Requirements](#requirements)
@@ -247,6 +249,45 @@ to the user.
 If no middleware manages the error, the lambda execution fails reporting the unmanaged error.
 
 
+### Async Middlewares
+
+Middy supports middlewares that return promises instead that directly calling the callback:
+
+```javascript
+const asyncValidator = () => {
+  before: (handler) => {
+    if (handler.event.body) {
+      return new Promise((resolve, reject) => {
+        // async validation logic
+      })
+    }
+
+    return Promise.resolve()
+  }
+}
+
+handler.use(asyncValidator())
+```
+
+Thanks to this behaviour you can define middlewares using `async` functions:
+
+```javascript
+const asyncValidator = () => {
+  before: async (handler) => {
+    if (handler.event.body) {
+      return await asyncValidate(handler.event.body)
+    }
+
+    return
+  }
+}
+
+handler.use(asyncValidator())
+```
+
+Of course, since AWS lambda runs on Node.js 6.10, you will need to transpile your `async/await` code (e.g. using [babel](https://babeljs.io/)).
+
+
 ## Writing a middleware
 
 A middleware is an object that should contain at least 1 of 3 possible keys:
@@ -440,7 +481,7 @@ Middy factory function. Use it to wrap your existing handler to enable middlewar
 | before | [<code>middlewareAttachFunction</code>](#middlewareAttachFunction) | attach a new *before-only* middleware |
 | after | [<code>middlewareAttachFunction</code>](#middlewareAttachFunction) | attach a new *after-only* middleware |
 | onError | [<code>middlewareAttachFunction</code>](#middlewareAttachFunction) | attach a new *error-handler-only* middleware |
-| __middlewares | <code>Object</code> | contains the list of all the attached    middlewares organised by type (`before`, `after`, `onError`). To be used only   for testing and debugging purposes |
+| __middlewares | <code>Object</code> | contains the list of all the attached   middlewares organised by type (`before`, `after`, `onError`). To be used only   for testing and debugging purposes |
 
 <a name="useFunction"></a>
 

README.md.hb

@@ -23,6 +23,9 @@
   <a href="https://standardjs.com/">
     <img src="https://img.shields.io/badge/code_style-standard-brightgreen.svg" alt="Standard Code Style"  style="max-width:100%;">
   </a>
+  <a href="https://greenkeeper.io/">
+    <img src="https://badges.greenkeeper.io/middyjs/middy.svg" alt="Greenkeeper badge"  style="max-width:100%;">
+  </a>
   <a href="https://gitter.im/middyjs">
     <img src="https://badges.gitter.im/gitterHQ/gitter.svg" alt="Chat on Gitter"  style="max-width:100%;">
   </a>
@@ -246,6 +249,45 @@ to the user.
 If no middleware manages the error, the lambda execution fails reporting the unmanaged error.
 
 
+### Async Middlewares
+
+Middy supports middlewares that return promises instead that directly calling the callback:
+
+```javascript
+const asyncValidator = () => {
+  before: (handler) => {
+    if (handler.event.body) {
+      return new Promise((resolve, reject) => {
+        // async validation logic
+      })
+    }
+
+    return Promise.resolve()
+  }
+}
+
+handler.use(asyncValidator())
+```
+
+Thanks to this behaviour you can define middlewares using `async` functions:
+
+```javascript
+const asyncValidator = () => {
+  before: async (handler) => {
+    if (handler.event.body) {
+      return await asyncValidate(handler.event.body)
+    }
+
+    return
+  }
+}
+
+handler.use(asyncValidator())
+```
+
+Of course, since AWS lambda runs on Node.js 6.10, you will need to transpile your `async/await` code (e.g. using [babel](https://babeljs.io/)).
+
+
 ## Writing a middleware
 
 A middleware is an object that should contain at least 1 of 3 possible keys: