It's all about optimization

2.7.0 Javascript on Demand

Javascript On Demand (JOD) is a technique of loading only the scripts that are necessary for the functionality of your page, and doing this asynchronously only if they are needed.

This can be achieved by splitting your massive function library into small modules, and loading these using a "bootstrap". It's a fairly advanced technique that creates some complex script interdependencies, but this is made easier via AJAX functions available in many popular Javascript libraries.

The spirit of JOD is to save the client from downloading massive function libraries when they only need a very small portion of the functionality within.