User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/534.24 (KHTML, like Gecko) Chrome/11.0.696.14 Safari/534.24 Build Identifier: 4.0 Just try a setTimeout(alert,5); alert will return a number value, but no param are expected here W3C say "This method calls the function once after a specified number of milliseconds elapses, until canceled by a call to clearTimeout. The methods returns a timerID which may be used in a subsequent call to clearTimeout to cancel the interval." http://www.w3.org/TR/Window/ Reproducible: Always