This script implements a register of calls in order to have guarded access on a (shared) single dom element. In particular, the flash message div (user notification banner) should only fade out if the last user notification has been displayed for 5-6 secs

gistfile1.js

// Module that encapsulates access to numberOfCalls and numberOfCompletedCalls.
// Facilitates the ensurance that every flash message is displayed for 5-6 sec.
// Use registerOne() to register a flash message (before calling fade!).
// Use completeOne() once to indicate that a flash message has passed its display time.
// Use allowFade() in order to ask whether the flash div can be faded out now.
Register = function () {
  var numberOfCalls = 0;
  var numberOfCompletedCalls = 0;
  
  return {
    registerOne: function() {
      numberOfCalls++;
    },
    completeOne: function() {
      numberOfCompletedCalls++;
    },
    allowFade: function() {
      return (numberOfCalls == numberOfCompletedCalls);
    }
  };
};

RegisterOfCalls = Register();

// Call guardedFade() in order to ensure that the flash message is displayed for 5-6 sec.
function guardedFade() {
  return function() {
    RegisterOfCalls.completeOne();
    tryFade();
  }.delay(5);
}

// tryFade polls for the allowance to fade out the flash div.
function tryFade() {  
  return function() {
    if(RegisterOfCalls.allowFade()) {
      Effect.Fade('flash', { duration: 0.5 });
    } else {
      tryFade();
    }
  }.delay(1); 
}

// displays flash message by replacing the existing flash div
function flash(flash_div) {
  RegisterOfCalls.registerOne();
  
  var id = 'flash';
  $(id).replace(flash_div);
  // TODO schmidt: document this. How does the div get displayed? Is the flash message displayed at all in IE 7.0?
  if (navigator.userAgent.indexOf("MSIE 7.0") == -1) {
    Effect.Appear(id, { duration: 0.5 });
  }
  
  guardedFade();
}

// hides the unobtrusive flash message on page load (if javascript enabled)
// calls the initial flash method
function initial_hide() {
  var id = 'flash_unobtrusive';
  if($(id)) {
    $(id).hide();
    // get existing message and interaction class
    flashMessage($(id).innerHTML, getInteractionClass(id));
  }
}

function flashMessage(message, type) {
  // default: type = notice
  type = typeof(type) != 'undefined' ? type : 'notice';
  var id = 'flash';
  // build flash_div and call flash()
  flash("<div id='" + id + "' class='" + type + "'>" + message + "</div>");
}

function getInteractionClass(id) {
  return $(id).hasClassName('error') ? 'error' : ($(id).hasClassName('success') ? 'success' : 'notice')
}