This document discusses how JavaScript and the way web applications are built have changed from 1999 to the present. It covers the evolution of JavaScript versions and libraries/patterns like JSON, AJAX, MVC, modules, prototypes, closures, IIFEs, and event emitters. The document emphasizes that applications should be built with loosely coupled and independent modules to improve reusability and avoid unintended changes. It provides some references on large scale app architecture patterns and custom events in JavaScript.