mala/app.js

## app.js
var express = require("express");
var app = express();
var expressWs = require('express-ws')(app);

app.use(express.static(__dirname + '/public'));
app.listen(3000, function () {
  console.log('Example app listening on port 3000!');
});
app.ws('/state', function(ws, req) {
  ws.on('message', function(msg) {
    expressWs.getWss().clients.forEach(client => client.send(msg));
  });
});

## index.html
<html>
<head>
  <title>presen tool</title>
  <link rel="stylesheet" href="presen.css">
</head>
<body>
<div id="slide"></div>
<script src="marked.js"></script>
<script>
function Presen(filename){
  var data;
  var state = { _page: 0 };
  Object.defineProperty(state, "page", {
    get: () => state._page,
    set: (v) => { state._page = v; update() }
  });

  var update = function(){
    console.log(state.page);
    var src = data[state.page] || "";
    var html = marked(src);
    document.getElementById("slide").innerHTML = html;
  };

  var init = function(){
    fetch(filename).then(res => res.text()).then(text => {
      data = text.split("----");
      update();
    });
  };

  var connected = false;
  var ws;
  var start_watcher = function(){
    if (connected) return;
    ws = new WebSocket("ws://" + location.host + "/state");
    ws.onopen = e => {
      connected = true;
      ws.onmessage = e => {
        console.log(e);
        var message = JSON.parse(e.data);
        console.log(message);
        state.page = message._page;
      };
    };
    ws.onclose = e => {
      connected = false;
    };
  };

  var key_listener = function(){
    document.onkeydown = (e) => {
      console.log(e.keyCode);
      if (e.keyCode == 39 || e.keyCode == 40) { state.page++}
      if (e.keyCode == 37 || e.keyCode == 38) { state.page--}
      ws.send(JSON.stringify(state));
    }
  };

  key_listener();
  setInterval(start_watcher, 1000);
  init();
}
var url = (location.hash.indexOf("en") != -1) ? "main_en.txt" : "main.txt";
Presen(url);
</script>
</body>
</html>
	var express = require("express");
	var app = express();
	var expressWs = require('express-ws')(app);

	app.use(express.static(__dirname + '/public'));
	app.listen(3000, function () {
	console.log('Example app listening on port 3000!');
	});
	app.ws('/state', function(ws, req) {
	ws.on('message', function(msg) {
	expressWs.getWss().clients.forEach(client => client.send(msg));
	});
	});
	<html>
	<head>
	<title>presen tool</title>
	<link rel="stylesheet" href="presen.css">
	</head>
	<body>
	<div id="slide"></div>
	<script src="marked.js"></script>
	<script>
	function Presen(filename){
	var data;
	var state = { _page: 0 };
	Object.defineProperty(state, "page", {
	get: () => state._page,
	set: (v) => { state._page = v; update() }
	});

	var update = function(){
	console.log(state.page);
	var src = data[state.page] \|\| "";
	var html = marked(src);
	document.getElementById("slide").innerHTML = html;
	};

	var init = function(){
	fetch(filename).then(res => res.text()).then(text => {
	data = text.split("----");
	update();
	});
	};

	var connected = false;
	var ws;
	var start_watcher = function(){
	if (connected) return;
	ws = new WebSocket("ws://" + location.host + "/state");
	ws.onopen = e => {
	connected = true;
	ws.onmessage = e => {
	console.log(e);
	var message = JSON.parse(e.data);
	console.log(message);
	state.page = message._page;
	};
	};
	ws.onclose = e => {
	connected = false;
	};
	};

	var key_listener = function(){
	document.onkeydown = (e) => {
	console.log(e.keyCode);
	if (e.keyCode == 39 \|\| e.keyCode == 40) { state.page++}
	if (e.keyCode == 37 \|\| e.keyCode == 38) { state.page--}
	ws.send(JSON.stringify(state));
	}
	};

	key_listener();
	setInterval(start_watcher, 1000);
	init();
	}
	var url = (location.hash.indexOf("en") != -1) ? "main_en.txt" : "main.txt";
	Presen(url);
	</script>
	</body>
	</html>