prototype/src/ajax.js

var Ajax = {
  getTransport: function() {
    return Try.these(
      function() {return new XMLHttpRequest()},
      function() {return new ActiveXObject('Msxml2.XMLHTTP')},
      function() {return new ActiveXObject('Microsoft.XMLHTTP')}
    ) || false;
  },
  
  activeRequestCount: 0
}

Ajax.Responders = {
  responders: [],
  
  _each: function(iterator) {
    this.responders._each(iterator);
  },

  register: function(responder) {
    if (!this.include(responder))
      this.responders.push(responder);
  },
  
  unregister: function(responder) {
    this.responders = this.responders.without(responder);
  },
  
  dispatch: function(callback, request, transport, json) {
    this.each(function(responder) {
      if (typeof responder[callback] == 'function') {
        try {
          responder[callback].apply(responder, [request, transport, json]);
        } catch (e) {}
      }
    });
  }
};

Object.extend(Ajax.Responders, Enumerable);

Ajax.Responders.register({
  onCreate: function() {
    Ajax.activeRequestCount++;
  }, 
  onComplete: function() {
    Ajax.activeRequestCount--;
  }
});

Ajax.Base = function() {};
Ajax.Base.prototype = {
  setOptions: function(options) {
    this.options = {
      method:       'post',
      asynchronous: true,
      contentType:  'application/x-www-form-urlencoded',
      encoding:     'UTF-8',
      parameters:   ''
    }
    Object.extend(this.options, options || {});
    
    this.options.method = this.options.method.toLowerCase();
    if (typeof this.options.parameters == 'string') 
      this.options.parameters = this.options.parameters.toQueryParams();
  }
}

Ajax.Request = Class.create();
Ajax.Request.Events = 
  ['Uninitialized', 'Loading', 'Loaded', 'Interactive', 'Complete'];

Ajax.Request.prototype = Object.extend(new Ajax.Base(), {
  _complete: false,
  
  initialize: function(url, options) {
    this.transport = Ajax.getTransport();
    this.setOptions(options);
    this.request(url);
  },

  request: function(url) {
    this.url = url;
    this.method = this.options.method;
    var params = Object.clone(this.options.parameters);

    if (!['get', 'post'].include(this.method)) {
      // simulate other verbs over post
      params['_method'] = this.method;
      this.method = 'post';
    }
    
    this.parameters = params;

    if (params = Hash.toQueryString(params)) {
      // when GET, append parameters to URL
      if (this.method == 'get')
        this.url += (this.url.include('?') ? '&' : '?') + params;
      else if (/Konqueror|Safari|KHTML/.test(navigator.userAgent))
        params += '&_=';
    }
      
    try {
      if (this.options.onCreate) this.options.onCreate(this.transport);
      Ajax.Responders.dispatch('onCreate', this, this.transport);
    
      this.transport.open(this.method.toUpperCase(), this.url, 
        this.options.asynchronous);

      if (this.options.asynchronous) this.respondToReadyState.bind(this).defer(1);
      
      this.transport.onreadystatechange = this.onStateChange.bind(this);
      this.setRequestHeaders();

      this.body = this.method == 'post' ? (this.options.postBody || params) : null;
      this.transport.send(this.body);

      /* Force Firefox to handle ready state 4 for synchronous requests */
      if (!this.options.asynchronous && this.transport.overrideMimeType)
        this.onStateChange();
        
    }
    catch (e) {
      this.dispatchException(e);
    }
  },

  onStateChange: function() {
    var readyState = this.transport.readyState;
    if (readyState > 1 && !((readyState == 4) && this._complete))
      this.respondToReadyState(this.transport.readyState);
  },
  
  setRequestHeaders: function() {
    var headers = {
      'X-Requested-With': 'XMLHttpRequest',
      'X-Prototype-Version': Prototype.Version,
      'Accept': 'text/javascript, text/html, application/xml, text/xml, */*'
    };

    if (this.method == 'post') {
      headers['Content-type'] = this.options.contentType +
        (this.options.encoding ? '; charset=' + this.options.encoding : '');
      
      /* Force "Connection: close" for older Mozilla browsers to work
       * around a bug where XMLHttpRequest sends an incorrect
       * Content-length header. See Mozilla Bugzilla #246651. 
       */
      if (this.transport.overrideMimeType &&
          (navigator.userAgent.match(/Gecko\/(\d{4})/) || [0,2005])[1] < 2005)
            headers['Connection'] = 'close';
    }
    
    // user-defined headers
    if (typeof this.options.requestHeaders == 'object') {
      var extras = this.options.requestHeaders;

      if (typeof extras.push == 'function')
        for (var i = 0, length = extras.length; i < length; i += 2) 
          headers[extras[i]] = extras[i+1];
      else
        $H(extras).each(function(pair) { headers[pair.key] = pair.value });
    }

    for (var name in headers) 
      this.transport.setRequestHeader(name, headers[name]);
  },
  
  success: function() {
    return !this.transport.status
        || (this.transport.status >= 200 && this.transport.status < 300);
  },

  respondToReadyState: function(readyState) {
    var state = Ajax.Request.Events[readyState];
    var transport = this.transport, json = this.evalJSON();

    if (state == 'Complete') {
      try {
        this._complete = true;
        (this.options['on' + this.transport.status]
         || this.options['on' + (this.success() ? 'Success' : 'Failure')]
         || Prototype.emptyFunction)(transport, json);
      } catch (e) {
        this.dispatchException(e);
      }
      
      var contentType = this.getHeader('Content-type');
      if (contentType && contentType.strip().
        match(/^(text|application)\/(x-)?(java|ecma)script(;.*)?$/i))
          this.evalResponse();
    }

    try {
      (this.options['on' + state] || Prototype.emptyFunction)(transport, json);
      Ajax.Responders.dispatch('on' + state, this, transport, json);
    } catch (e) {
      this.dispatchException(e);
    }
    
    if (state == 'Complete') {
      // avoid memory leak in MSIE: clean up
      this.transport.onreadystatechange = Prototype.emptyFunction;
    }
  },
  
  getHeader: function(name) {
    try {
      return this.transport.getResponseHeader(name);
    } catch (e) { return null }
  },
  
  evalJSON: function() {
    try {
      var json = this.getHeader('X-JSON');
      return json ? json.evalJSON() : null;
    } catch (e) { return null }
  },
  
  evalResponse: function() {
    try {
      return eval((this.transport.responseText || '').unfilterJSON());
    } catch (e) {
      this.dispatchException(e);
    }
  },

  dispatchException: function(exception) {
    (this.options.onException || Prototype.emptyFunction)(this, exception);
    Ajax.Responders.dispatch('onException', this, exception);
  }
});

Ajax.Updater = Class.create();

Object.extend(Object.extend(Ajax.Updater.prototype, Ajax.Request.prototype), {
  initialize: function(container, url, options) {
    this.container = {
      success: (container.success || container),
      failure: (container.failure || (container.success ? null : container))
    }
    
    this.transport = Ajax.getTransport();
    this.setOptions(options);

    var onComplete = this.options.onComplete || Prototype.emptyFunction;
    this.options.onComplete = (function(transport, param) {
      this.updateContent();
      onComplete(transport, param);
    }).bind(this);

    this.request(url);
  },

  updateContent: function() {
    var receiver = this.container[this.success() ? 'success' : 'failure'];
    var response = this.transport.responseText, options = this.options;
    
    if (!options.evalScripts) response = response.stripScripts();
    
    if (receiver = $(receiver)) {
      if (options.insertion) {
        if (typeof options.insertion == 'string')
          receiver.insert( {}[options.insertion] = response );
        else options.insertion(receiver, response);
      } 
      else receiver.update(response);
    }
    
    if (this.success()) {
      if (this.onComplete) this.onComplete.bind(this).defer();
    }
  }
});

Ajax.PeriodicalUpdater = Class.create();
Ajax.PeriodicalUpdater.prototype = Object.extend(new Ajax.Base(), {
  initialize: function(container, url, options) {
    this.setOptions(options);
    this.onComplete = this.options.onComplete;

    this.frequency = (this.options.frequency || 2);
    this.decay = (this.options.decay || 1);
    
    this.updater = {};
    this.container = container;
    this.url = url;

    this.start();
  },

  start: function() {
    this.options.onComplete = this.updateComplete.bind(this);
    this.onTimerEvent();
  },

  stop: function() {
    this.updater.options.onComplete = undefined;
    clearTimeout(this.timer);
    (this.onComplete || Prototype.emptyFunction).apply(this, arguments);
  },

  updateComplete: function(request) {
    if (this.options.decay) {
      this.decay = (request.responseText == this.lastText ? 
        this.decay * this.options.decay : 1);

      this.lastText = request.responseText;
    }
    this.timer = this.onTimerEvent.bind(this).delay(this.decay * this.frequency);
  },

  onTimerEvent: function() {
    this.updater = new Ajax.Updater(this.container, this.url, this.options);
  }
});