Queue Example for my blog

basic-log.js

function logEvent(eventData) {
  $.ajax({
    method: 'post',
    url: '/analytics-endpoint', 
    data: eventData
  });
}

persistent-queue.js

function readFromStorage(key) {
  var listString = window.localStorage.getItem(key)
    , list = listString && JSON.parse(listString)
    ;
  
  return list;
}

function writeToStorage(key, obj) {
  window.localStorage.setItem(key, obj);
}

function persistentQueue(name) {
  var prefix = 'persistentQueue:'
    , q
    , key = prefix + name
    ;
  
  q = queue(readFromStorage(key));
  q.onEnqueue = q.onDequeue = function (list) {
    writeToStorage(key, list);
  };
  
  return q;
}

qm-declaration.js

function queueManager(myQueue, callback) {
  //...

qm-fail.js

  function fail(message) {
    failCount += 1;
    me.onFail(myQueue.peek(), failCount);
    // try again
    process();
  }

qm-flush.js

  function flush() {
    if (!flushing) {
      flushing = true;
      process();
    }
  }

qm-next.js

  function next() {
    failCount = 0;
    myQueue.dequeue();
    me.onNext(myQueue.peek());
    process();
  }

qm-process.js

  function process() {
    if (myQueue.hasAny()) {
      callback(myQueue.peek(), next, fail);
    } else {
      // done
      flushing = false;
      me.onFlush();
    }
  }

qm-public.js

  return me = {
    flush: flush
    // hooks
  , onFail: function (item, count) { }
  , onNext: function (item) { }
  , onFlush: function () { }
  };

qm-start.js

  // start flushing whenever item is added to queue
  (function () {
    var old = myQueue.onEnqueue;
    myQueue.onEnqueue = function (list) {
      old(list);
      flush();
    };
  }());

queue-log.js

var analyticsEvents = queue()
  , qm;

qm = queueManager(analyticsEvents, function (eventData, next, fail) {
  $.ajax({
    method: 'post',
    url: '/analytics-endpoint', 
    data: eventData,
    success: next,
    error: fail
  });
});

function logEvent(eventData) {
  analyticsEvents.enqueue(eventData);
}

queue-manager-usage.js

var q = queue()
  , qm
  , counter = 0
  ;
  
qm = queueManager(q, function (item, next, fail) {
  // fail every other try
  counter += 1
  if (counter % 2 === 1) {
    console.log('Retrying ' + item);
    fail();
  } else {
    console.log(item + ' processed successfully.')
    next();
  }
});

q.enqueue('item1', 'item2');

// output:
// Retrying item1
// item1 processed successfully.
// Retrying item2
// item2 processed successfully.

queue-manager.js

function queueManager(myQueue, callback) {
  var flushing = false
    , me
    , failCount = 0
    ;

  function flush() {
    if (!flushing) {
      flushing = true;
      process();
    }
  }

  function process() {
    if (myQueue.hasAny()) {
      callback(myQueue.peek(), next, fail);
    } else {
      // done
      flushing = false;
      me.onFlush();
    }
  }

  function next() {
    failCount = 0;
    myQueue.dequeue();
    me.onNext(myQueue.peek());
    process();
  }

  function fail(message) {
    failCount += 1;
    me.onFail(myQueue.peek(), failCount);
    // try again
    process();
  }

  // start flushing whenever item is added to queue
  (function () {
    var old = myQueue.onEnqueue;
    myQueue.onEnqueue = function (list) {
      old(list);
      flush();
    };
  }());

  return me = {
    flush: flush
    // hooks
  , onFail: function (item, count) { }
  , onNext: function (item) { }
  , onFlush: function () { }
  };
}

queue-usage.js

var myQueue = queue();

// use the hooks to print status to the console
myQueue.onEnqueue = function (list) { console.log(list); }
myQueue.onDequeue = function (list) { console.log(list); }

queue.hasAny(); // false
// call enqueue to add values
queue.enqueue(1);
// [1]
queue.enqueue(2, 3);
// [1, 2, 3]
queue.hasAny(); // true

// call dequeue to remove values
var item = queue.dequeue();
// [2, 3]
console.log(item); // 1

// call peek to view an item without removing it
item = queue.peek();
console.log(item); // 2

queue.all(); // [2, 3]

queue.js

function queue(list) {
  var me;

  list = list || [];

  return me = {
    enqueue: function () {
      var args = Array.prototype.slice.call(arguments)
        , i, ii
        ;

      for (i = 0, ii = args.length; i < ii; i++) {
        list.push(args[i]);
      }

      me.onEnqueue(me.all());
    }

  , dequeue: function (callback) {
      var value = list.shift();
      me.onDequeue(me.all());

      return value;
    }

  , peek: function () {
      return list[0];
    }

  , all: function () {
      // return a copy of the list
      return list.slice(0);
    }

  , hasAny: function () {
      return list.length > 0;
    }
  // hooks
  , onEnqueue: function (list) { }
  , onDequeue: function (list) { }
  };
}

stored-queue-log.js

var analyticsEvents = persistentQueue('analytics')
  , qm;

qm = queueManager(analyticsEvents, function (eventData, next, fail) {
  $.ajax({
    method: 'post',
    url: '/analytics-endpoint', 
    data: eventData,
    success: next,
    error: fail
  });
});

function logEvent(eventData) {
  analyticsEvents.enqueue(eventData);
}