Getting started

  1. How KO works and what benefits it brings
  2. Downloading and installing


  1. Creating view models with observables
  2. Working with observable arrays

Computed observables

  1. Using computed observables
  2. Writable computed observables
  3. How dependency tracking works
  4. Pure computed observables
  5. Reference


Controlling text and appearance

  1. The visible and hidden bindings
  2. The text binding
  3. The html binding
  4. The class and css bindings
  5. The style binding
  6. The attr binding

Control flow

  1. The foreach binding
  2. The if and ifnot bindings
  3. The with and using bindings
  4. The let binding
  5. The component binding
  6. Binding lifecycle events

Working with form fields

  1. The click binding
  2. The event binding
  3. The submit binding
  4. The enable and disable bindings
  5. The value binding
  6. The textInput binding
  7. The hasFocus binding
  8. The checked binding
  9. The options binding
  10. The selectedOptions binding
  11. The uniqueName binding

Rendering templates

  1. The template binding

Binding syntax

  1. The data-bind syntax
  2. The binding context

Creating custom bindings

  1. Creating custom bindings
  2. Controlling descendant bindings
  3. Supporting virtual elements
  4. Custom disposal logic
  5. Preprocessing: Extending the binding syntax


  1. Overview: What components and custom elements offer
  2. Defining and registering components
  3. The component binding
  4. Using custom elements
  5. Advanced: Custom component loaders

Further techniques

  1. Loading and saving JSON data
  2. Extending observables
  3. Deferred updates
  4. Rate-limiting observables
  5. Unobtrusive event handling
  6. Using fn to add custom functions
  7. Microtasks
  8. Asynchronous error handling


  1. The mapping plugin

More information

  1. Browser support
  2. Getting help
  3. Links to tutorials & examples
  4. Usage with AMD using RequireJs (Asynchronous Module Definition)

The "attr" binding


The attr binding provides a generic way to set the value of any attribute for the associated DOM element. This is useful, for example, when you need to set the title attribute of an element, the src of an img tag, or the href of a link based on values in your view model, with the attribute value being updated automatically whenever the corresponding model property changes.


<a data-bind="attr: { href: url, title: details }">

<script type="text/javascript">
    var viewModel = {
        url: ko.observable("year-end.html"),
        details: ko.observable("Report including final year-end statistics")

This will set the element’s href attribute to year-end.html and the element’s title attribute to Report including final year-end statistics.


  • Main parameter

    You should pass a JavaScript object in which the property names correspond to attribute names, and the values correspond to the attribute values you wish to apply.

    If your parameter references an observable value, the binding will update the attribute whenever the observable value changes. If the parameter doesn’t reference an observable value, it will only set the attribute once and will not update it later.

  • Additional parameters

    • None

If you want to apply the attribute data-something, you can’t write this:

<div data-bind="attr: { data-something: someValue }">...</div>

… because data-something isn’t a legal identifier name at that point. The solution is simple: just wrap the identifier name in quotes so that it becomes a string literal, which is legal in a JavaScript object literal. For example,

<div data-bind="attr: { 'data-something': someValue }">...</div>

Note: Setting attributes with a namespace

The attr binding can be used to set attributes that include a namespace, such as xlink:href:

<a data-bind="attr: { 'xlink:href': href }">
    <ellipse data-bind="attr: red" />

Note: Using reserved words as attribute names in older browsers

In older browsers (ie8 and below) using reserved javascript words as attribute names causes an error. You can get around this by quoting them like this:

<input data-bind="attr: { 'for': someValue }" />

You can find a good list of reserved words on Mozilla’s MDN page here.


None, other than the core Knockout library.