Purpose 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. Example <a data-bind="attr: { href: url, title: details }"> Report </a> <script type="text/java

Note: This documentation applies to Knockout 3.4.0 and later. ko.onError Knockout wraps internal asynchronous calls and looks for an optional ko.onError callback to execute, if an exception is encountered, before throwing the original error. This gives you the opportunity to run custom logic, such as passing the error to a logging module. Additionally, since the original call is wrapped in a try/catch, the error passed to ko.onError contains a stack property, which is not true in many browsers