What is the difference between a view model and a model in KnockoutJS?

Question

Aryan Kumar · Answer

In Knockout.js, the terms "view model" and "model" refer to different concepts within the context of the MVVM (Model-View-ViewModel) architecture. Here's a breakdown of the key differences between a view model and a model in Knockout.js:
Model:
Definition:
The model represents the data and business logic of your application. It typically consists of plain JavaScript objects or data structures that hold information relevant to your application's domain.
Responsibility:
The model is responsible for managing and manipulating the data, as well as implementing any business rules or logic. It does not contain any knowledge about the presentation or user interface.
Observable Properties:
While models in Knockout.js don't have to be observables, it's common to use observables within the model if you want to take advantage of two-way data binding. However, the use of observables in models is not a strict requirement.
Example:
An example of a model could be a simple JavaScript object representing a user:
function UserModel(name, age) {
    this.name = ko.observable(name);
    this.age = ko.observable(age);
}
View Model:
Definition:
The view model is a layer that sits between the model and the view. It acts as an adapter, transforming the raw data from the model into a form that is suitable for presentation in the view. The view model often includes additional functionality, such as computed observables and methods, to support the presentation layer.
Responsibility:
The view model is responsible for exposing the necessary data and behavior to the view, making it a bridge between the raw data in the model and the user interface. It may also include logic for handling user interactions, form submissions, and other view-related concerns.
Observable Properties:
View models often use observables extensively to achieve two-way data binding with the view. Observables in the view model automatically update the view when the underlying data changes and vice versa.
Example:
An example of a view model could be a ViewModel that wraps around the UserModel mentioned earlier:
function UserViewModel(name, age) {
    this.user = new UserModel(name, age);
    this.formattedAge = ko.computed(function () {
        return this.user.age() + ' years old';
    }, this);
}
In summary, the model represents the data and business logic, while the view model acts as an intermediary that adapts the data for presentation in the view. Both models and view models can use Knockout.js observables, but the key distinction lies in their roles within the MVVM architecture.

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What is the difference between a view model and a model in KnockoutJS?

Revati S Misra

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