WebWorkerPool.js

const Pool = function(size) {
  this.taskQueue = [];
  this.workerQueue = [];
  this.poolSize = size;
};


Pool.prototype.addWorkerTask = function(workerTask) {
  if (this.workerQueue.length > 0) {
    let workerThread = this.workerQueue.shift();
    workerThread.run(workerTask);
  } else {
    this.taskQueue.push(workerTask);
  }
};


Pool.prototype.init = function init() {
  for (let i = 0 ; i < this.poolSize ; i++) {
    this.workerQueue.push(new WorkerThread(this));
  }
};


Pool.prototype.freeWorkerThread = function(workerThread) {
  if (this.taskQueue.length > 0) {
    let workerTask = this.taskQueue.shift();
    workerThread.run(workerTask);
  } else {
    this.taskQueue.push(workerThread);
  }
};


const WorkerThread = function(parentPool) {
  this.parentPool = parentPool;
  this.workerTask = {}; 
};

WorkerThread.prototype.run = function(workerTask) {
  this.workerTask = workerTask;
  if (this.workerTask.script != null) {
    let worker = new Worker(this.workerTask.script);
    worker.addEventListener('message', this.dummyCallback.bind(this));
    worker.postMessage(this.workerTask.startMessage);
  }
};


WorkerThread.prototype.dummyCallback = function(event) {
  this.workerTask.callback(event);
  this.parentPool.freeWorkerThread(this);
};


const WorkerTask = function (script, callback, msg) {
  this.script = script;
  this.callback = callback;
  this.startMessage = msg;
};