context of fx function (#223)

examples/functions/JavaScript/README.md

@@ -0,0 +1,33 @@
+# Make a JavaScript function a service with fx
+
+Write a function like,
+
+```JavaScript
+module.exports = (ctx) => {
+  ctx.body = 'hello world'
+}
+```
+
+then deploy it with `fx up` command,
+
+```shell
+$ fx up -p 8080:3000 func.js
+```
+
+test it using `curl`
+
+```shell
+$ curl 127.0.0.1:8080
+
+HTTP/1.1 200 OK
+Connection: keep-alive
+Content-Length: 11
+Content-Type: text/plain; charset=utf-8
+Date: Tue, 06 Aug 2019 15:58:41 GMT
+
+hello world
+```
+
+### ctx
+
+The `ctx` object is exactly the [ctx](https://github.com/koajs/koa/blob/master/docs/api/context.md) of [Koa](https://github.com/koajs/koa)