Access window object from a different js file

I have a web worker that generates pdf of a table and post it on the main js file. The code is something like this

worker.js

onmessage = function(e) {
    var pdf = window.generatePdf();
    postMessage(e.data[0]);
}

main.js

var worker = new Worker('worker.js');
worker.postMessage([config]);
worker.onmessage = function(e) {
  save(e.data);
}

But window object can no be accessed in worker.js file. Any idea on how to make it accessible in that file or how to achieve the functionality otherwise. Thaks