title: Do browsers parse javascript on every page load?
body: <p>Do browsers (IE and Firefox) parse linked javascript files every time the page refreshes?</p>
  
  <p>They can cache the files, so I'm guessing they won't try to download them each time, but as each page is essentially separate, I expect them to tear down any old code and re-parse it.</p>
  
  <p>This is inefficient, although perfectly understandable, but I wonder if modern browsers are clever enough to avoid the parsing step within sites. I'm thinking of cases where a site uses a javascript library, like ExtJS or jQuery, etc.</p>