Javascript shouldn't be a problem for slower internet connections, it can be even useful by loading only the necessary parts of the site when users navigate. One problem is that lot of sites are using multiple libraries and widgets. Other problem is with web applications that show a loading screen (Gmail too) before showing the interface. The first load of most web applications should be static HTML, and JS should be run only after the first state of the interface is rendered. The worse is when the page loads the HTML and then the JS and then JS makes other request(s) to load more content for the first page.