This book shows how to build front-end web applications with plain JavaScript, not using any (third-party) framework or library. A front-end web application can be provided by any web server, but it is executed on the user's computer device (smartphone, tablet or notebook), and not on the remote web server. Typically, but not necessarily, a front-end web application is a single-user application, which is not shared with other users. Content: I. Associations　　　 20. Reference Properties and Unidirectional Associations　　　 21. Implementing Unidirectional Functional Associations　　　 22. Implementing Unidirectional Non-Functional Associations　　　 23. Practice Projects　　　 24. Bidirectional Associations　　　 25. Implementing Bidirectional Associations　　　 26. Part-Whole Associations　　　 27. Lessons Learned　　　 28. Practice ProjectsII. Inheritance in Class Hierarchies　　　 29. Subtyping and Inheritance　　　 30. Implementing Class Hierarchies in a Plain JavaScript Front-End App　　　 31. Implementing Class Hierarchies in a Java EE Back-End App　　　 32. Practice ProjectsIII. Model-Based App Development