Purpose The value binding links the associated DOM element’s value with a property on your view model. This is typically useful with form elements such as <input>, <select> and <textarea>. When the user edits the value in the associated form control, it updates the value on your view model. Likewise, when you update the value in your view model, this updates the value of the form control on screen. Note: If you’re working with checkboxes or radio buttons, use the checked bindi

Knockout is built around three core features: Observables and dependency tracking Declarative bindings Templating On this page, you’ll learn about the first of these three. But before that, let’s examine the MVVM pattern and the concept of a view model. MVVM and View Models Model-View-View Model (MVVM) is a design pattern for building user interfaces. It describes how you can keep a potentially sophisticated UI simple by splitting it into three parts: A model: your application’s stored data.

Note: This documentation applies to Knockout 3.4.0 and later. For previous versions, the Deferred Updates plugin provides similar support. In complex applications, with multiple, intertwined dependencies, updating a single observable might trigger a cascade of computed observables, manual subscriptions, and UI binding updates. These updates can be expensive and inefficient if unnecessary intermediate values are pushed to the view or result in extra computed observable evaluations. Even in a sim

Purpose The click binding adds an event handler so that your chosen JavaScript function will be invoked when the associated DOM element is clicked. This is most commonly used with elements like button, input, and a, but actually works with any visible DOM element. Example <div> You've clicked <span data-bind="text: numberOfClicks"></span> times <button data-bind="click: incrementClickCounter">Click me</button> </div> <script type="text/javascript"

If you want to detect and respond to changes on one object, you’d use observables. If you want to detect and respond to changes of a collection of things, use an observableArray. This is useful in many scenarios where you’re displaying or editing multiple values and need repeated sections of UI to appear and disappear as items are added and removed. Example var myObservableArray = ko.observableArray(); // Initially an empty array myObservableArray.push('Some value'); // Adds the v

In most cases, data-bind attributes provide a clean and succinct way to bind to a view model. However, event handling is one area that can often result in verbose data-bind attributes, as anonymous functions were typically the recommended techinique to pass arguments. For example: <a href="#" data-bind="click: function() { viewModel.items.remove($data); }"> remove </a> As an alternative, Knockout provides two helper functions that allow you to identify the data associated with

Whenever you inject a component using the component binding or a custom element, Knockout fetches that component’s template and viewmodel using one or more component loaders. The job of a component loader is to asynchronously supply a template/viewmodel pair for any given component name. The default component loader Component loader utility functions Implementing a custom component loader Functions you can implement getConfig(name, callback) loadComponent(name, componentConfig, callback) load

Purpose The event binding allows you to add an event handler for a specified event so that your chosen JavaScript function will be invoked when that event is triggered for the associated DOM element. This can be used to bind to any event, such as keypress, mouseover or mouseout. Example <div> <div data-bind="event: { mouseover: enableDetails, mouseout: disableDetails }"> Mouse over me </div> <div data-bind="visible: detailsEnabled"> Details

Pure computed observables, introduced in Knockout 3.2.0, provide performance and memory benefits over regular computed observables for most applications. This is because a pure computed observable doesn’t maintain subscriptions to its dependencies when it has no subscribers itself. This feature: Prevents memory leaks from computed observables that are no longer referenced in an application but whose dependencies still exist. Reduces computation overhead by not re-calculating computed observab

Purpose The textInput binding links a text box (<input>) or text area (<textarea>) with a viewmodel property, providing two-way updates between the viewmodel property and the element’s value. Unlike the value binding, textInput provides instant updates from the DOM for all types of user input, including autocomplete, drag-and-drop, and clipboard events. Example <p>Login name: <input data-bind="textInput: userName" /></p> <p>Password: <input type="password"