Javascript: Printing to Console from Web Worker

main.js

// create the worker object
var worker = new Worker( "worker.js" );

// add message event listener
worker.addEventListener( 'message', function( event ) {
  switch ( event.data.type ) {
  case "debug":
    console.log( event.data.message );
    break;
  case "result":
    // process event.data.value
    break;
  }
};

// add error event listener
worker.addEventListener( 'error', function( e ) {
  console.log( "Worker Error: " + e );
});

var data = {}; // holds the data to be passed to worker
worker.postMessage( data );

worker.js

// add message event listener
self.addEventListener( 'message', function( event ) {
  // process the data and return the result
  self.postMessage({
    type: 'result',
    value: process( event.data )
  });
};

// process the data
var process = function( data ){
  var result;
  
  self.postMessage({
    type: "debug",
    message: "Processing Started."
  });
  
  // compute result
  
  return result;
}