Internet Explorer doesn’t use JavaScript. Instead, it uses their own creation called JScript which is supposed to be the same, but has some bugs in it.
var a = function b(){ return typeof b; };
alert(a())
returns function in all browsers
//
alert(typeof a)
returns function in all browsers
//
alert(a() === typeof a)
returns true in all browsers.
However,
var a = function b() { return b; };
returns function b() { return b; }
alert(a() === a ); fails in IE, probably because the layout of the two functions is not exactly the same. You can see this if you look at the return info.