const Range = length => [...Array(length).keys()];
const data = Range(10000);
const workers = Range(5).map(_ => new Worker('worker.js'));
for(let worker of workers){
  worker.onmessage = res => {
    if(data.length)
        res.target.postMessage(data.shift());
    else
        res.target.terminate();
  };
  worker.postMessage(data.shift());
}