Some Questions About The Typeof Operator Of IE9

I have been learning the Definitive Guide of JavaScript.i got a question about the typeof opertor. I run the script 'alert(typeof window.alert)' in IE9 it proved to be return 'fun

Solution 1:

IE<=8 used to have peculiar object bindings, and the typeof operator returned object where it should have returned function.

Removing the doctype puts IE into quirks mode. This makes sure that older websites can be viewed and older scripts don't throw errors.

Solution 2:

I found this to be a good explanation:

http://www.w3.org/QA/Tips/Doctype