Introduction - If you have any usage issues, please Google them yourself
A Web page can load a lot faster and feel faster if the JavaScript files referenced on the page can be loaded after the visible content has been loaded and multiple JavaScript files can be batched into one download. Browsers download one external JavaScript at a time and sometimes pause rendering while a script is being downloaded and executed. This makes Web pages load and render slowly when there are multiple external JavaScript references on the page. For every JavaScript reference, the browser stops downloading and processing of any other content on the page and some browsers (like Internet Explorer 6) pause rendering while it processes the JavaScript. This gives a slow loading experience and the Web page kind of gets stuck frequently. As a result, a Web page can only load fast when there are small number of external scripts on the page and the scripts are loaded after the visible content of the page has loaded.