What does leaving 'www' out of an address do?

[Redline]

I don't really get why leaving the 'www' prefix out of an address
#1 still leads you to the site you're trying to get to
#2 but breaks certain javascript functions

I'm building a shopping cart with php/mysql/javascript and ajax. I'm using ajax to update item quantities, but when I leave the 'www' out, and the script tries to write the updated price to the page, permission is denied.

[teknomage1]

The way the internet works is a little confusing because of an inverse hierarchial decision that was made for the addressing. Basically after the 'http://' part until the first '/' you have things listed from most specific to least and after the slash you have things listed from least specific to greatest. So for the example in the url http://www.example.com/bigfolder/littlefolder/somepage.html . You can think of .com as representing a root of a tree containing every .com address (google, miscrosoft, codenewbie, etc) , the example tells the browser where to look for a machine called 'www' . In a lot of cases the machine www is the machine pointed to by the root url. That's why you go to the same place. The path /bigfolder/littlefolder/somepage.html refers to a file on www.

As to why it breaks javascript, I assume there's some bad validation happening.

[nimaj]

or javascript is looking for a cookie belonging to 'www.whatever.something'.