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,
  });
};