The proper format is
Basically, you’re telling jQuery not do do any work yet (DOM manipulation, i.e. page manipulation) untill the whole html page has loaded completely, finished and ready.
On a small simple page, this may not be a problem. But for a large page that’s pulling content from different places, it may take a few seconds before the page finishes loading. (and if user has a slow browser, internet connection, then it’s even important for you to wait until the page has finished loading.)