While JavaScript can be used to enhance your visitors' experience of your Joomla! website, it can have a negative impact in terms of both real and envisaged loading times of pages.
JavaScript slows down the loading of a page because it's a single-threaded language. This means that nothing else can occur while JavaScript is being loaded or something in JavaScript is being evaluated. As such, a single, slow-loading JavaScript file can prevent a whole website from loading quickly!
1. The most obvious thing that you can do to make your Joomla! template load more efficiently is to compress any JavaScript you do use. As such, there are a number of online compression tools that you can use, including the JavaScript Compressor (http://javascriptcompressor.com):

2. Once you've inserted your JavaScript into the Paste your code input area, click on Compress. In this example, we've used a function that creates a slideshow...