Best way to check for IE less than 9 in JavaScript without library

Question

What would be your fastest, shortest (best) way to detect browser which is IE and version less than 9 in JavaScript, without using jQuery or any add-on libraries?

Answer 1

Below is an improvement over James Padolsey's solution:

1) It doesn't pollute memory (James' snippet creates 7 unremoved document fragments when detecting IE11, for example).
2) It's faster since it checks for a documentMode value before generating markup.
3) It's far more legible, especially to beginning JavaScript programmers.

Gist link: https://gist.github.com/julianshapiro/9098609

/*
 - Behavior: For IE8+, we detect the documentMode value provided by Microsoft.
 - Behavior: For  0; i--) {
            var div = document.createElement("div");

            div.innerHTML = "";

            if (div.getElementsByTagName("span").length) {
                return i;
            }
        }
    }

    return undefined;
})();