What is the MVVM architectural pattern?

Model-View-ViewModel. The pattern separates the user interface (View) and business logic (Model) with an intermediate layer called ViewModel.

• Model: Represents data and business logic. It is UI-independent.
• View: Displays data from the ViewModel and sends user actions to the ViewModel. It contains no business logic.
• ViewModel: Contains data and logic for the View, transforming Model data into a format suitable for display. It notifies the View of data changes and handles user actions by interacting with the Model.

Advantages of MVVM:

• Separation of concerns: Clearly separates UI, display logic, and business logic.
• Testability: ViewModel is easy to test independently of the UI.
• Maintainability: Changes in UI or business logic less frequently affect each other.
• Reusability: ViewModel can be used by different Views.
• Data Binding: Simplifies synchronization between the View and ViewModel.

Usage in Frontend:

Used in frameworks like Vue.js, React (with some adaptations, such as using hooks and state managers), Angular (which is close to MVVM in essence).

Example (simplified Vue.js):

// Model
class User {
  constructor(name) {
    this.name = name;
  }
}

// ViewModel
class UserViewModel {
  constructor(user) {
    this.userName = user.name; // Transformation for display
  }

  updateName(newName) {
    // Update logic, possibly interacting with the model
    this.userName = newName;
  }
}

// View (Vue component)
// <template>
//   <div>
//     <h1>{{ viewModel.userName }}</h1>
//     <input v-model="viewModel.userName" @input="viewModel.updateName($event.target.value)">
//   </div>
// </template>

// <script>
// export default {
//   data() {
//     const user = new User('John Doe'); // Creating model
//     const viewModel = new UserViewModel(user); // Creating ViewModel
//     return {
//       viewModel
//     };
//   }
// }
// </script>