Extending OpenLayers 3

In the previous examples, we worked hard to reduce the size of the library by cutting out some irrelevant parts. Now, let's do the contrary and extend the library with additional functionality. Remember the example where we measured distance on an ellipsoid? We used the debug library of an older OpenLayers 3 version to achieve this. Now, we will build the ol.Ellipsoid class in our next custom build. You can find a JavaScript file, named ellipsoid.js, in the examples folder and an example named ch10_test_ellispsoid. The latter is the exact copy of ch05_measure with ch05_measure_vincenty.js. First, open up ellipsoid.js. This is how a well-structured code looks from the aspect of the Closure Compiler. There are headers everywhere with type definitions and additional information. These headers are written in the syntax of JSDoc, but JSDoc and Closure Compiler go hand in hand.

The first part of the code resolves the dependencies of this constructor and provides a name for...