A Task Queue, because sometimes I don't want to learn another API

example.js

var tasks = new TaskQueue(5);
tasks.queue(getUrl.bind(null, 'google.com'))
tasks.queue(getUrl.bind(null, 'yahoo.com'))
tasks.queue(getUrl.bind(null, 'facebook.com'))
tasks.next() // kick it.

function getUrl(url, cb) {
  magicalXHR(url, cb);
}

TaskQueue.js

function TaskQueue(concurrency) {
  var _queue = [];
  var _concurrents = 0;
  var ctr = {
    queue: function(fn) {
      _queue.push(fn)
    },
    next: function() {
      while (_concurrents < concurrency) {
        _concurrents += 1;
        var t = _queue.shift();
        if (!t) return;
        t(function() {
          _concurrents -= 1;
          ctr.next();
        });
      }
    }
  }

  return ctr;
}