app/index.html

<html>
  <head>
    <title>SSH Terminal</title>
    <link rel="stylesheet" href="/xterm.css" />
    <script src="/xterm.js"></script>
    <script src="/xterm-addon-fit.js"></script>
    <script src="/socket.io/socket.io.js"></script>
    <script>
      window.addEventListener('load', function() {
        var terminalContainer = document.getElementById('terminal-container');
        const term = new Terminal({ cursorBlink: true });        
        const fitAddon = new FitAddon.FitAddon();
        term.loadAddon(fitAddon);
        term.open(terminalContainer);
        fitAddon.fit();

        var socket = io() //.connect();
        socket.on('connect', function() {
          term.write('\r\n*** Connected to backend ***\r\n');
        });

        // Browser -> Backend
        term.onKey(function (ev) {
          socket.emit('data', ev.key);
        });

        // Backend -> Browser
        socket.on('data', function(data) {
          term.write(data);
        });

        socket.on('disconnect', function() {
          term.write('\r\n*** Disconnected from backend ***\r\n');
        });
      }, false);
    </script>
    <style>
      body {
        font-family: helvetica, sans-serif, arial;
        font-size: 1em;
        color: #111;
      }
      h1 {
        text-align: center;
      }
      #terminal-container {
        width: 960px;
        height: 600px;
        margin: 0 auto;
        padding: 2px;
      }
      #terminal-container .terminal {
        background-color: #111;
        color: #fafafa;
        padding: 2px;
      }
      #terminal-container .terminal:focus .terminal-cursor {
        background-color: #fafafa;
      }
    </style>
  </head>
  <body>
    <h3>WebSSH</h3>
    <div id="terminal-container"></div>
  </body>
</html>