How to change browser User-Agent Header with javaScript?

Question

Following code changes property printed (when accessed through javaScript) by browser console and not the actual Use-Agent string sent with the header.

Object.defineProperty(navigator, 'userAgent', {
    get: function () { return 'Mozilla/5.0 (Windows NT 6.2; WOW64; 
    rv:28.0) Gecko/20100101 Firefox/28.0)'; }
});

Answer 1

This is now possible to do, see: https://developer.mozilla.org/en-US/docs/Glossary/Forbidden_header_name You can use ‘ XMLHttpRequest.setRequestHeader(User-Agent, value)’

Answer 2

This isn't possible from the page itself. The user agent string (as sent in the HTTP request headers) can only be changed via browser extension or browser configuration.