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