window.onload = function() {
  console.group("Playing with console.log()");
  console.log("A firebug console message");
  console.log(2, "firebug", "messages");
  console.log("%d firebug messages", 3);
  console.log("A div element:", $("message"));
  console.groupEnd();

  console.group("Playing with console.<error-level>()");
  console.debug("A normal log message.");
  console.debug("Just some debugging.");
  console.info("Here's some info for you.");
  console.warn("I'm warning you!");
  console.error("Error. That's just great.");
  console.groupEnd();

  console.group("Assertions");
  console.assert(1==1);
  console.assert(1==2);
  console.groupEnd();

  console.group("Handling a real error");
  makeARealError();
  console.groupEnd();
}

function makeARealError() {
  var x = 1+2+3+undefinedVar;
}