OpenLayers provides an easy way to create a custom build of the library to include in your page that contains only the things you need. Throughout this book, we've been including a file called ol.js (or ol-debug.js), a file that contains all the functionality (classes, functions, and so on) that OpenLayers provides. So far, this has been great—we've been developing up to this point, so we want to be sure that we have access to all the classes that we may use.
Well, the ol.js file we've been using is around 391 KB, and the debug version is 3.5 MB! Both are quite large files to load, especially since they contain only JavaScript code. Even though large file sizes aren't as much of an issue as they were years ago, when everyone was on slower connections, a large JavaScript file in a production environment is something we want to avoid if at all possible. This is especially true for mobile environments, where users pay for data plans and data...