webworker

main.js

/*
Question: I need to access to the web worker's onmessage data somehow
*/
var worker = new Worker('worker.js');

var file = {
  createReadStream: function() {
    worker.postMessage(options); // some sort of options
  
    worker.onmessage = function(e) {
      // this has to be outside?
      // can't make async to sync so..
      var stream = e.data; 
    }
    // has to return stream HERE
  }
};

worker.js

self.onmessage = function(e) {
  var options = e.data;
  var stream = getStreamObjectSomehow(options);
  postMesage(stream);
};

Here's another workaround, using the Promise object.

var worker = new Worker('worker.js');

var file = {
  createReadStream: function() {
    worker.postMessage(options); // some sort of options

    // sorta impossible to make an async function synchronous, so.... promises, promises, promises...
    var promise = new Promise(function(resolve, reject) {
      worker.onmessage = function(e) {
        var stream = e.data;
        resolve(stream)
      };
      worker.onerror = function(e) {
        reject(e.data)
      }
    });
    // return a Promise object, instead of a stream
    return promise;
  }
};
file.createReadStream().then(function(stream) { console.log(stream) }).catch(function(err) { console.log(err) });