gecko-dev/dom/workers/test/consoleReplaceable_worker.js

/**
 * Any copyright is dedicated to the Public Domain.
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

onmessage = function(event) {
  postMessage({event: 'console exists', status: !!console, last : false});
  var logCalled = false;
  console.log = function() {
    logCalled = true;
  }
  console.log("foo");
  postMessage({event: 'console.log is replaceable', status: logCalled, last: false});
  console = 42;
  postMessage({event: 'console is replaceable', status: console === 42, last : true});
}