Knockout JS Interview Questions and Answers for 7 years experience

0
KnockoutJS Interview Questions and Answers

  1. What is KnockoutJS and why would you use it?

    • Answer: KnockoutJS is a JavaScript library that helps create rich, dynamic user interfaces with a clean underlying data model. It uses the Model-View-ViewModel (MVVM) pattern to separate concerns, making code more maintainable and testable. We use it to easily bind data to HTML elements, enabling automatic updates whenever the underlying data changes, reducing the amount of manual DOM manipulation.

  2. Explain the MVVM pattern in the context of KnockoutJS.

    • Answer: In KnockoutJS, the Model represents the data, the View is the HTML user interface, and the ViewModel acts as an intermediary. The ViewModel observes changes in the Model and updates the View accordingly. It also handles user interactions in the View, updating the Model as needed. This separation simplifies development and testing.

  3. How do you create an observable in KnockoutJS? Give examples of different observable types.

    • Answer: You create an observable using the `ko.observable()` function. For example: `let myObservable = ko.observable("Initial Value");`. Knockout offers various observable types: `ko.observable()`, `ko.observableArray()`, `ko.computed()`, `ko.observableArray().push()`, `ko.observableArray().splice()` etc. `ko.observableArray()` is for arrays, and `ko.computed()` creates dependent observables that automatically update when their dependencies change.

  4. Explain the difference between `ko.observable` and `ko.computed`.

    • Answer: `ko.observable` holds a single value and notifies subscribers when its value changes. `ko.computed` is a read-only observable that depends on other observables. Whenever a dependency changes, the computed observable automatically recalculates and notifies its subscribers. It's ideal for derived data.

  5. How do you bind data to HTML elements using KnockoutJS? Provide examples of different binding handlers.

    • Answer: Data binding is done using data-bind attributes within HTML elements. Examples include `text`, `html`, `visible`, `css`, `style`, `click`, `foreach`, `with`, etc. For example: `` binds the text content of the span to the value of `myObservable`. `foreach` iterates over arrays, `with` creates a context, `click` handles events.

  6. Explain the `ko.applyBindings` function.

    • Answer: `ko.applyBindings(viewModel)` applies KnockoutJS bindings to a specified DOM element (defaults to the entire document). It links the provided `viewModel` object to the HTML elements, enabling data binding and the automatic updates.

  7. What are KnockoutJS templates and how do you use them?

    • Answer: KnockoutJS templates allow you to reuse sections of HTML, especially useful with `foreach` to render lists of items. They are defined using the `