OpenLayers is a big and complex framework. There is no other option available for a framework that allows working with many GIS standards, reading from many different data sources, rendering on different browser technologies, and so on. This power comes with a price.

The implementation of OpenLayers tries to have as less dependencies on external libraries as possible. This means, OpenLayers requires implementing many features that we can find in other projects: DOM elements' manipulation, AJAX requests, and so on.

This chapter shows some of these features, in addition to other possible common needs we can require in our day-to-day work that are not explained in other chapters, such as creation of layer animations or the implementation of custom controls. Because of this, the chapter is more suited for more experienced JavaScript programmers.