Before getting started

In the previous chapters, we discussed the HTML and CSS parts quite thoroughly. From now on, we will focus on the JavaScript part of the application. We will use native JavaScript (no jQuery, ExtJS, or other libraries) to build our application. This way, we will have a better understanding of the native language, rather than a library's abstraction methods. Eventually, our code will be more verbose, but this is a price we are willing to pay in order to gain better insight into JavaScript.

Using a proxy

For this chapter, I have adapted a simple Python proxy file to use from the one made by the OpenLayers Contributors for OpenLayers 2. As we will use AJAX requests to fetch features and metadata, we can easily bump into real CORS restrictions. These restrictions can only be resolved by a server-side proxy script, which requests the data from the target server and forwards it to us. From this moment on, the data will be from the same origin as the proxy script on...