Emitting events

The main idea behind Socket.IO is that you can send and receive any events you want, with any data you want. Any objects that can be encoded as JSON will do, and binary data is supported too.

Let’s make it so that when the user types in a message, the server gets it as a chat message event. The script section in index.html should now look as follows:

ES6

<script src="/socket.io/socket.io.js"></script>
<script>
  const socket = io();

  const form = document.getElementById('form');
  const input = document.getElementById('input');

  form.addEventListener('submit', (e) => {
    e.preventDefault();
    if (input.value) {
      socket.emit('chat message', input.value);
      input.value = '';
    }
  });
</script>

ES5

<script src="/socket.io/socket.io.js"></script>
<script>
  var socket = io();

  var form = document.getElementById('form');
  var input = document.getElementById('input');

  form.addEventListener('submit', function(e) {
    e.preventDefault();
    if (input.value) {
      socket.emit('chat message', input.value);
      input.value = '';
    }
  });
</script>

And in index.js we print out the chat message event:

io.on('connection', (socket) => {
  socket.on('chat message', (msg) => {
    console.log('message: ' + msg);
  });
});

The result should be like the following video:

info

CommonJS

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ES modules

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