console.log() in IE9 only works when the console is open!
console.log() first made an appearance in Firefox's Firebug (or at least that is when I first noticed it) and has been in most major browsers, including Internet Explorer since version 8. Whilst developing, I have happily had my console open so I can debug things.
On production, we were getting some weird bugs with IE9 and I could not for the life of me figure them out because every time I opened the console, lo and behold, they disappeared. This was driving me nuts!
I opened the console to check, and it went away. I closed the console again but I still didn't see the error. Curious...
Anyways, after some googling, I found that console.log() does not work in IE if the console has not been opened.
Anyways, I basically got around it by creating a mock console object if the console is not present.
So there you have it...