A data model organizes the information an application manages and provides a usable interface to that information. In an MVC-style design, the model holds data, the view presents it, and the controller coordinates changes between them. section 14.4
Keeping data inside a rendering component makes ownership unclear and editing harder. Moving exercise data into a separate model gives components a central place to read, add, edit, clear, save, and load application state. section 14.4
Central workout-plan model
A shared WorkoutPlanData object stores the current workout, uses localStorage for named plans, and exposes save, load, clear, and playback methods. The exercise library imports the model and adds serialized exercises to it; controls call the same model rather than duplicating state logic. section 14.5
