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?

<script type="text/javascript">
    var a = [59, 20, 75, 22, 20, 11, 63, 29, 15, 77]; 
    var result = a.indexOf(32);//
    document.write(result);
</script>

Error message as below:

SCRIPT438: Object doesn't support property or method 'indexOf' 

test.php, line 9 character 1

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.

Answer 2

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.

Answer 3

It might help if you declare the array explicitly:

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