In the first version of TodoIt, the model was almost non-existent:

• There were no classes or interfaces.
• All the logic was held in functions within todo-it.ts.
• The state was stored in a global variable.

Also, the todo items only had a description.

Now that we have reviewed the major OO building blocks, the UML, and the class diagrams, let's use our newly acquired skills to help us visualize our target domain model. Let's imagine how we could leverage classes and interfaces to organize things a bit better and improve the quality of our application code.