Considering some techniques to load scripts in parallel so that the overall download time becomes the longest of all instead of the sum of all downloads. The simplest way you can do this is through a programmatically created <script> element. You do this using code, as shown below.
var h = document.getElementsByTagName("HEAD")[0];
var script = document.createElement("script");
script.type = "text/javascript";
script.onreadystatechange = function() {...};
script.onload = function() {...};
script.onerror = function() {...};
document.src = "...";
h.appendChild(script)
Script elements are appended to the HEAD element so that parallel download begins as soon as possible. Note that this is the approach that most social Web sites and Google Analytics use internally. The net effect is that all dynamically created elements are processed on different JavaScript threads. This approach is also employed by some popular JavaScript loader frameworks these days.