Creating a basic chatbar?

Below is old; look at the updated text at the bottom.

So my friends and I use google docs to communicate while in school, and we setup the challenge to create a working and "efficient" chat bar to communicate with better results. I've been around JavaScript for quite some time, but have never fooled around with Google Apps Script before. We are using the document app for our chats; the code I came up with is as below, but I have a few problems with it:

Errors when a user closes it, then goes to Chat -> Open Chat in the toolbar to re-open, saying, "Error encountered: An unexpected error occurred"; does not specify a line or reason
Needs a hidden element somewhere in the document which can allow users to see what others have typed, but that they can't edit without using the chat box (would add event listener to update chat box when text is ammended)

//Main function, ran when the document first opens.
function onOpen() {
    var app = UiApp.createApplication(); //Create a Ui App to use for the chat bar

    if(getCurrentUser()=="dev1"||getCurrentUser()=="dev2"){ //user-Id's hidden for privacy
        DocumentApp.getUi().createMenu('Chat')
          .addItem('AutoColor', 'autoColor')
          .addItem('Open Chat', 'createChatBox')
          .addItem('Elements', 'displayElements') //Hidden as it is not important for regular use
          .addItem('MyID', 'showUser')
          .addToUi();
    }else{
        DocumentApp.getUi().createMenu('Chat')
          .addItem('AutoColor', 'autoColor')
          .addItem('Open Chat', 'createChatBox')
          .addToUi();
   }
}

//Creates and returns the chats GUI
function createChatBox(){
    var app = UiApp.getActiveApplication()
    app.setTitle("Chat Bar (not yet working)");
    var vPanel = app.createVerticalPanel().setId('chatPanel').setWidth('100%');
    var textArea = app.createTextArea().setId('chatBox').setName('chatBox').setReadOnly(true).setText('').setSize('250px', '450px'); //Read only so they can not edit the text, even if it won't affect overall chat
    var textBox = app.createTextBox().setId('messageBox').setName('messageBox').setText('Words');
    var chatHandler = app.createServerHandler("sayChat").addCallbackElement(textArea).addCallbackElement(textBox);
    var chatButton = app.createButton().setId("sayButton").setText("Say!").addMouseUpHandler(chatHandler);

    vPanel.add(textArea);
    vPanel.add(textBox);
    vPanel.add(chatButton);

    app.add(vPanel);
    DocumentApp.getUi().showSidebar(app);
    return app;
}

//The event handler for when the "Say!" (post) button is pressed. Is probably where the conflict stems from.
function sayChat(eventInfo){
    var app = UiApp.getActiveApplication();
    var parameter = eventInfo.parameter;

    app.getElementById("chatBox").setText(parameter.chatBox+"["+getCurrentUser()+"]: "+parameter.messageBox);
    app.getElementById("messageBox").setText("");

    return app;
}

//A debug function and a function to tell you the unique part of your email (useless, really)
function showUser(){
    DocumentApp.getUi().alert("Your userId is: "+getCurrentUser());
}

//Returns the unique part of a person's email; if their email is "magicuser@gmail.com", it returns "magicuser"
function getCurrentUser(){
    var email = Session.getActiveUser().getEmail();
    return email.substring(0,email.indexOf("@"));
}
//The Auto-color and displayElements methods are hidden as they contain other user-info. They both work as intended and are not part of the issue.

I do not need someone to rewrite the code (although that'd be greatly appreciated!), but instead point out what I'm doing wrong or suggest something to change/add.

Last, before you suggest it, the google docs chat does not work with our computers. It is not the fault of the document, but probably a compatability error with our browser. It is because of this issue that we are going through this fun yet hasty process of making our own chat method.

Update

I decided to give up on my version of the chat using pure Google Apps Script and help improve my friends version using both G-A-S and HTML. I added image thumbnail/linking support with command /img or /image, along with improved time and counter, and some other behind the scenes updates. Here is a quick screenshot of it:

Magnificent chat programmed from scratch, and no buggy update methods, just a casual refresh database to check for messages and set HTML text-area text. No more buggy getText methods. For each new message in the database, whether targeted toward the user or toward everyone in the chat, we load all the database messages up to a limit (50 messages at a time), then display them. The use of HTML in the messages is key to its appearence and features, such as images.

function getChat() {
  var chat = "";
  var time = getTime();

  var username = getCurrentUsername();

  var db = ScriptDb.getMyDb();
  var query = db.query({time : db.greaterThan(getJoinTime())}).sortBy('time', db.DESCENDING).limit(50);

  var flag = query.getSize() % 2 != 0;

  while(query.hasNext()) {
    var record = query.next();
    if(record.showTo == "all" || record.showTo == getCurrentUsername()) {
      var text = record.text;
      for(var i = 0; i < text.split(" ").length; i++) {
        var substr = text.split(" ")[i];
        if(substr.indexOf("http://") == 0 || substr.indexOf("https://") == 0) {
          text = text.replace(substr, "<a href='" + substr + "'>" + substr + "</a>");
        }
      }
      var message = "<pre style='display:inline;'><span class='" + (flag? "even" : "odd") + "'><b>[" + record.realTime + "]</b>" + text;
      message += "</span></pre>";
      chat += message;
      flag = !flag;
    }
  }
  //DocumentApp.getUi().alert(getTime() - time);

  return chat;
}

I am going to re-do his getChat() method to only check for new messages, and not load every message at each refresh.

First thing to to to get rid of your error message is to create the UiApp in the createChat function instead of onOpen.

I also used a client handler to clear the textBox because it's just more efficient. Here is the modified code :

code removed see updates below

As for your second request I'm not sure I understand exactly what you want to do... could you explain more precisely the behavior you expect ? (this is more a comment than an answer but I used the "answer field" to be more readable)

EDIT : I played a little with this code and came to something that -almost- works... it still needs to be improved but it's worth showing how it works.

I used scriptProperties to store the common part of the conversation, I think that's a good approach but the issue it to know when to update its content. Here is the code I have so far, I keep being open to any suggestion/improvement of course.

code removed, new version below

EDIT 2 : here is a version with an auto update that works quite good, the script updates the chat area automatically for a certain time... if no activity then it stops and wait for a user action. please test (using 2 accounts) and let us know what you think.

note I used a checkBox to handler the autoUpdate, I keep it visible for test purpose but of course it could be hidden in a final version.

EDIT 3 : added a message to warn the user when he's been put offline + changed textBox to colored textArea to allow for longer messages + condition to clear the messageBox so that the warning message doesn't go in the conversation. (set the time out to a very short value for test purpose, change the counter value to restore to your needs)

function onOpen() {

    if(getCurrentUser()=="dev1"||getCurrentUser()=="dev2"){ //user-Id's hidden for privacy
        DocumentApp.getUi().createMenu('Chat')
          .addItem('AutoColor', 'autoColor')
          .addItem('Open Chat', 'createChatBox')
          .addItem('Elements', 'displayElements') //Hidden as it is not important for regular use
          .addItem('MyID', 'showUser')
          .addToUi();
    }else{
        DocumentApp.getUi().createMenu('Chat')
          .addItem('AutoColor', 'autoColor')
          .addItem('Open Chat', 'createChatBox')
          .addToUi();
   }
}

function createChatBox(){
  ScriptProperties.setProperty('chatContent','');
  var app = UiApp.createApplication().setWidth(252);
  app.setTitle("Chat Bar");
  var vPanel = app.createVerticalPanel().setId('chatPanel').setWidth('100%');
  var chatHandler = app.createServerHandler("sayChat").addCallbackElement(vPanel);
  var textArea = app.createTextArea().setId('chatBox').setName('chatBox').setReadOnly(true).setText('').setSize('250px', '450px');
  var textBox = app.createTextArea().setId('messageBox').setName('messageBox').setText('Start chat...').setPixelSize(250,100).setStyleAttributes({'padding':'5px','background':'#ffffcc'}).addKeyPressHandler(chatHandler);
  var clearTextBoxClientHandler = app.createClientHandler().forTargets(textBox).setText('');
  textBox.addClickHandler(clearTextBoxClientHandler);
  var chatButton = app.createButton().setId("sayButton").setText("Say!").addMouseUpHandler(chatHandler);
  var chkHandler = app.createServerHandler('autoUpdate').addCallbackElement(vPanel);
  var chk = app.createCheckBox().setId('chk').addValueChangeHandler(chkHandler);
  vPanel.add(textArea);
  vPanel.add(textBox);
  vPanel.add(chatButton);
  vPanel.add(chk);
  app.add(vPanel);
  DocumentApp.getUi().showSidebar(app);
  return app;
}

function sayChat(e){
  var app = UiApp.getActiveApplication();  
  var user = '['+getCurrentUser()+'] : ';
  if(e.parameter.messageBox=="You have been put offline because you didn't type anything for more than 5 minutes..., please click here to refresh the conversation"){
    app.getElementById('messageBox').setText('');// clear messageBox
    ScriptProperties.setProperty('chatTimer',0);// reset counter
    return app;
  }
  if(e.parameter.source=='messageBox'&&e.parameter.keyCode!=13){return app};
  var content = ScriptProperties.getProperty('chatContent');
  ScriptProperties.setProperty('chatContent',content+"\n"+user+e.parameter.messageBox)
  app.getElementById("chatBox").setText(content+"\n"+user+e.parameter.messageBox+'\n');
  app.getElementById('messageBox').setText('');
  app.getElementById('chk').setValue(true,true);
  ScriptProperties.setProperty('chatTimer',0);
  return app;
}

function autoUpdate(){
  var app = UiApp.getActiveApplication();
  var content = ScriptProperties.getProperty('chatContent');
  var counter = Number(ScriptProperties.getProperty('chatTimer'));
  ++counter;
  if(counter>20){
    app.getElementById('chk').setValue(false);
    app.getElementById('messageBox').setText("You have been put offline because you didn't type anything for more than 5 minutes..., please click here to refresh the conversation");
    return app;
  }
  ScriptProperties.setProperty('chatTimer',counter);
  var content = ScriptProperties.getProperty('chatContent');
  app.getElementById("chatBox").setText(content+'*'); // the * is there only for test purpose
  app.getElementById('chk').setValue(false);
  Utilities.sleep(750);
  app.getElementById('chk').setValue(true,true).setText('timer = '+counter);
  return app;
}

function showUser(){
  DocumentApp.getUi().alert("Your userId is: "+getCurrentUser());
}

function getCurrentUser(){
  var email = Session.getEffectiveUser().getEmail();
  return email.substring(0,email.indexOf("@"));
}