queued ajax requests with a queueMaxConcurrency option that can be set on each request

jquery.ajax.queue.coffee

$ = jQuery

queues  = {}

queue = (name) ->
  name = 'default' if name is true
  queues[name] or= {entries: [], running: 0}

next = (name, done) ->
  list = queue(name)

  if done
    queue(name).running--

  unless list.entries.length
    return

  [options, deferred] = list.entries[0]

  if list.running >= (options.queueMaxConcurrency || 1)
    return

  list.entries.shift()

  queue(name).running++

  $.ajax(options)
  .always(-> next(name, true))
  .done(-> deferred.resolve(arguments...))
  .fail(-> deferred.reject(arguments...))

push = (name, options) ->
  list = queue(name)
  deferred = $.Deferred()

  list.entries.push([options, deferred])
  next(name)
  deferred.promise()

remove = (name, options) ->
  list = queue(name)

  for [value, _], i in list.entries when value is options
    list.entries.splice(i, 1)
    break

$.ajaxTransport '+*', (options) ->
  if options.queue
    queuedOptions = $.extend({}, options)
    queuedOptions.queue = false
    queuedOptions.processData = false

    send: (headers, complete) ->
      push(options.queue, queuedOptions)
      .done (data, textStatus, jqXHR) ->
        complete(jqXHR.status,
          jqXHR.statusText,
          text: jqXHR.responseText,
          jqXHR.getAllResponseHeaders())

      .fail (jqXHR, textStatus, errorThrown) ->
        complete(jqXHR.status,
          jqXHR.statusText,
          text: jqXHR.responseText,
          jqXHR.getAllResponseHeaders())

    abort: ->
      remove(options.queue, queuedOptions)

jquery.ajax.queue.js

// Generated by CoffeeScript 1.6.2
(function() {
  var $, next, push, queue, queues, remove, running;

  $ = jQuery;

  queues = {};

  running = false;

  queue = function(name) {
    if (name === true) {
      name = 'default';
    }
    return queues[name] || (queues[name] = []);
  };

  next = function(name) {
    var deferred, list, options, _ref;

    list = queue(name);
    if (!list.length) {
      running = false;
      return;
    }
    _ref = list.shift(), options = _ref[0], deferred = _ref[1];
    return $.ajax(options).always(function() {
      return next(name);
    }).done(function() {
      return deferred.resolve.apply(deferred, arguments);
    }).fail(function() {
      return deferred.reject.apply(deferred, arguments);
    });
  };

  push = function(name, options) {
    var deferred, list;

    list = queue(name);
    deferred = $.Deferred();
    list.push([options, deferred]);
    if (!running) {
      next(name);
    }
    running = true;
    return deferred.promise();
  };

  remove = function(name, options) {
    var i, list, value, _, _i, _len, _ref, _results;

    list = queue(name);
    _results = [];
    for (i = _i = 0, _len = list.length; _i < _len; i = ++_i) {
      _ref = list[i], value = _ref[0], _ = _ref[1];
      if (!(value === options)) {
        continue;
      }
      list.splice(i, 1);
      break;
    }
    return _results;
  };

  $.ajaxTransport('+*', function(options) {
    var queuedOptions;

    if (options.queue) {
      queuedOptions = $.extend({}, options);
      queuedOptions.queue = false;
      queuedOptions.processData = false;
      return {
        send: function(headers, complete) {
          return push(options.queue, queuedOptions).done(function(data, textStatus, jqXHR) {
            return complete(jqXHR.status, jqXHR.statusText, {
              text: jqXHR.responseText
            }, jqXHR.getAllResponseHeaders());
          }).fail(function(jqXHR, textStatus, errorThrown) {
            return complete(jqXHR.status, jqXHR.statusText, {
              text: jqXHR.responseText
            }, jqXHR.getAllResponseHeaders());
          });
        },
        abort: function() {
          return remove(options.queue, queuedOptions);
        }
      };
    }
  });

}).call(this);