The HTTP/1.1 specification suggests that browsers download no more than two components in parallel per hostname. If you serve your images from multiple hostnames, you can get more than two downloads to occur in parallel. While a script is downloading, however, the browser won’t start any other downloads, even on different hostnames.
There are also ways to dynamically create SCRIPT nodes and load remote scripts after the page is loaded using AJAX .
Please note that, if users on your site have multiple page views per session and many of your pages re-use the same scripts and stylesheets, there is a greater potential benefit from cached external files.
Get rid of any Duplicate Scripts
Also, in many instances, though the scripts names are different, there is a likelihood of duplicate scripts within the same page due to team size and number of scripts.
Minimize accessing DOM elements where possible
• Cache references to accessed elements
• Update nodes “offline” and then add them to the tree
Separate Behavior from Content and Presentation