Generic self contained 'concurrent' worker in javascript

example.js

var request = require('request');
var genericMultiWorker = require('./genericmultiworker.js');
var TARGET_URL = 'http://example.com/';


// Example: POSTing to a URL with a maximum of 5 concurrent requests
var addToWorker = genericMultiWorker(5, function(obj, callback) {
  request.post(TARGET_URL, obj, callback);
});

// Example: populate queue with post request bodies
for (var i = 0; i < 1000; i++) {
  addToWorker({ example: 'content' });
}

genericmultiworker.js

/**
 * Generic 'concurrent' worker in javascript
 * @param  {Number}    Maximum simultaneous running functions
 * @param  {Function}  Function to use
 * @return {Function}  Adds an item to the queue of things being processed
 */
function genericMultiWorker(maxSimultaneous, func) {
  var queue = [];
  var pending = 0;

  function startIfFree() {
    if (pending >= maxPending || queue.length == 0) return;
    pending++;
    func(queue.shift(), function() {
      pending--;
      startIfFree(); 
    });
  }

  return function(item) {
    queue.push(item);
    startIfFree();    
  }  
}

module.exports = genericMultiWorker;