Q54: What are the restrictions of web workers on DOM - JavaScript Internals (521 Qs)

WebWorkers don't have access to below javascript objects since they are defined in an external files

Window object
Document object
Parent object

Practical Code Example

javascript

// Inside worker.js:
// document.getElementById('heading').textContent = 'Hi'; // ReferenceError: document is not defined!
// window.alert('Notice');                                // ReferenceError: window is not defined!

// Workers can only process data and send results back via postMessage:
self.onmessage = (event) => {
  const result = event.data * 2; // CPU computation
  self.postMessage(result);      // send back to main UI thread
};