Batch queue javascript

batchqueue.js

function BatchQueue(concurrentTasks) {
  this.concurrency = concurrentTasks;
  this.running = 0;
  this.queue = [];
}

BatchQueue.prototype.pushTask = function(task, callback) {
  this.queue.push(task);
  this.next();
}

BatchQueue.prototype.next = function() {
  var self = this;
  // while if were running and there are spots left and we have work
  // todo, do it. Shift work off the queue and execute the task
  while(self.running < self.concurrency && self.queue.length) {
    var task = self.queue.shift();
    task(function(err) {
      self.running--;
      self.next();
    });
    self.running++;
  }
}