add express example

examples/express-demo.md

@@ -0,0 +1,72 @@
+# Express client/server demo
+Example of node backend with express and client with fetch
+
+## Installation
+Install NPM packages
+`npm i -S express`
+`npm i -S body-parser`
+
+# Server
+```js
+//exec: /usr/local/opt/node@14/bin/node
+const express = require('express')
+const bodyParser = require('body-parser');
+const app = express()
+
+app.get('/', function (req, res) {
+  res.send('Hello World')
+})
+// POST HTML Form
+app.post('/subscribe', 
+    express.urlencoded({extended: true}), 
+    async (request, response) => {
+  print(`email ${request.body.email}`)
+  response.sendStatus(200);
+})
+
+// POST JSON data
+app.post('/activate', bodyParser.json(), async (request, response) => {
+  printJSON(request.body);
+  response.sendStatus(200);
+})
+
+app.listen(4000)
+```
+
+
+# Client
+## Post form with JS
+```js
+const data = new URLSearchParams();
+data.append('email', 'name@domain.com');
+
+const result = await fetch("http://localhost:4000/subscribe", {
+        body: data,
+        method: "post"
+});
+print(await result.text())
+```
+
+## Post form with HTML
+```html form
+    <form action="http://localhost:4000/contact" method="POST">
+        Email: <input type="text" name="email" id="email" required>
+        <button type="submit">Submit</button>
+    </form>
+```
+
+```js
+const form = loadBlock('form')
+print(form)
+```
+
+## POST JSON
+```js
+const data = {name: "Anthony"}
+const result = await fetch("http://localhost:4000/activate", {
+        body: JSON.stringify(data),
+        method: "post",
+        headers: {'Content-Type': 'application/json'}
+});
+print(await result.text())
+```