I notice this is the case mainly for rather sophisticated pages. However, why don't developers simply combine the JS files and condense it all together? Is it not a more efficient method, in terms of requests? I am not sure if it is but it would seem that way.
Why do many websites have so many javascript includes?
web development;website design;javascript
When talking about efficiency, as has been noted already, you've really got two issues.Efficiency in the development processEfficiency in delivering the site to the end userIt may perhaps be argued, but I think it fairly obvious that delivery is a higher priority. However when it comes to including scripts and dealing with changes in the site, having one massive 'god script' is a giant pain. Modularity is king of maintainability imho.One solution, like that mentioned by Ewan about Drupal, is to use your server-side language to dynamically 'compile' a JS file or two putting the whole mess together any time the code changes. Depending on how you achieve this it is possible to go ahead and use many sources during development and only one or a small number of them in production.There are also a few other practical matters to consider:You can offload some of your bandwidth for scripts that are hosted by services such as Google Libraries API or Yahoo's YUI. Increasingly, users have these files already onhand from other sites and, if nothing else, loading your site from more connections will speed up delivery.There are cases where you don't need the same functionality on every page and want to easily leave out some scripts while keeping the ones relevant to the current page.Every now and then you may actually want to load individual scripts after load-time using AJAX and whatnot based on the user's browsing context.