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

It might help if you declare the array explicitly:

var a = new Array(1,2,3);
a.indexOf(2);

Answer 2

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.

Answer 3

your code looks right and this compatibility table shows that IE9 should support indexOf() and checks your actual browser for compatibility.

try to open it and take a look at your result. maybe you're running you IE in compatibility mode for IE7/8 or something else.

this jsfiddle works in my IE9 - please try that, too.