IE9 array does not support indexOf

Question

Based on http://ie.microsoft.com/testdrive/HTML5/ECMAScript5Array/Default.html, I thought IE9 supports indexOf in array but the following breaks. Any idea why?

Answer 1

Are you sure your page is running in IE9 mode? Check in dev tools (F12). If you have old DOCTYPE you might be seeing your page in IE8/7 mode, so indexOf is not supported. If you are running in IE9 mode then it works just fine.