1. Function to String conversion produces different results in different browsers. var f = []['concat']; (f + ''); // Chrome "function concat() { [nativ

1. Function to String conversion produces different results in different browsers. var f = []['concat']; (f + ''); // Chrome "function concat() { [native code] }" // IE (9) " function concat() { [native code] } " This script tries to extract letters from that string representation, which fails if the string is different. (This is also used as an anti-debugging measure in some JS malware, to prevent researchers from replacing document.write with alert() or similar.) 2. Iterating over the window object doesn't work the same way in IE: http://blogs.msdn.com/b/ericlippert/archive/2005/05/04/414684.aspx http://blogs.msdn.com/b/ericlippert/archive/2005/05/04/41468... In particular, this script tries to extract strings 'sessionStorage', 'getComputedStyle', 'onchange' by iterating over the window object, all of whom fail in IE.