What is the architectural pattern MVVM?

MVVM (Model-View-ViewModel) is an architectural pattern that separates the user interface (View) from the business logic (Model) through an intermediate layer — the ViewModel.

Component	Description	Purpose
Model	Represents data and business rules.	Provides data, independent of View and ViewModel.
View	Displays the user interface.	Responsible for visualization and user interaction.
ViewModel	Contains presentation logic, translating data from Model for the View.	Connects View and Model, contains commands and properties for the View.

In MVVM, the connection between View and ViewModel is made through data binding mechanisms. The View "subscribes" to changes in ViewModel properties, and ViewModel notifies the View of these changes. User interactions with the View (e.g., clicking a button) initiate a command call in the ViewModel.

Advantages:

• Clear separation of responsibilities: UI, business logic, and presentation logic.
• Testability: ViewModel is easily testable independently of the View.
• Improved maintainability: Changes in one part of the system have less impact on others.
• Development: Frontend and backend developers can work in parallel.

Example of data binding concept (pseudocode):

// ViewModel
class CounterViewModel {
  count = 0; // observable property

  increment() {
    this.count++; // fires change notification
  }
}

// View (simplified representation)
<button onclick="viewModel.increment()">+</button>
<span data-bind="textContent: viewModel.count"></span> // Binds span content to viewModel.count