What restrictions are placed on the use of web worker threads?

• No direct access to the DOM.
• No access to global objects: window, document, parent.
• Limited access to browser APIs (e.g., no alert, confirm, prompt).
• Restrictions on working with certain built-in objects: XMLHttpRequest in synchronous mode.
• Data exchange only through messages (postMessage, onmessage) using structured cloning or transferable objects.
• Limited access to the file system (only via File API and Blob).
• Cannot create their own Web Workers.

// Example of restriction: no access to DOM from Worker
self.onmessage = function(e) {
  // The following line will cause an error because the worker does not have access to document
  // document.getElementById('result').textContent = e.data;

  // Instead, send the result back to the main thread
  self.postMessage('Processing completed: ' + e.data);
};