Simple chat using Firebase

#make a reference to your database

var messagesRef = new Firebase('https://<your url>.firebaseio.com/');

#cache frequent DOM references

var messageField = $('#messageInput'),
nameField = $('#nameInput'),
messageList = $('#messages'),
onlineList = $('#online-users');

#pressing enter will push our object (message) to our JSON  tree using the method push() and clear out input field

messageField.keypress(function (e) {
  if (e.keyCode == 13) {
    var username = nameField.val();
    var message = messageField.val();

    messagesRef.push({name:username, text:message});
    messageField.val('');
  }
});

#add a callback that gets data from each child object that  are created under its parent

  messagesRef.limitToLast(10).on('child_added', function (snapshot) {

    var data = snapshot.val();
    var username = data.name || "anonymous";
    var message = data.text;

#just to make sure we don't receive any empty messages  that have some how been triggered

    if (username && message) {

#creates our message and append it to our element

    var text = "says";
    var messageElement = $("<li>");
    var nameElement = $("<strong class='name'></strong>");
    nameElement.text(username.concat(' ' +text+ ' '));
    messageElement.text(message).prepend(nameElement);

    messageList.append(messageElement);

#scroll to bottom of list to display latest message

    messageList[0].scrollTop = messageList[0].scrollHeight;
  }
  });

#reference to a new data object where we will track presence in our channel

  var listRef = new Firebase("https://<your-url>.firebaseio.com/presence/");
  var userRef = listRef.push();

# add online user to presence list

  var presenceRef = new Firebase("https://<your-url>.firebaseio.com/.info/connected");
  presenceRef.on("value", function(snap) {
    if (snap.val()) {
      userRef.set(true);
      #remove user from preference list when disconnected by using the remove() method

      userRef.onDisconnect().remove();
    }
  });

#list our objects in presence list as online users in our   element

  listRef.on("value", function(snap) {

    onlineList.text(snap.numChildren());
  });