This directive sets the disabled attribute on the element if the expression inside ngDisabled evaluates to truthy.

A special directive is necessary because we cannot use interpolation inside the disabled attribute. The following example would make the button enabled on Chrome/Firefox but not on older IEs:

<!-- See below for an example of ng-disabled being used correctly -->
<div ng-init="isDisabled = false">
 <button disabled="{{isDisabled}}">Disabled</button>
</div>

This is because the HTML specification does not require browsers to preserve the values of boolean attributes such as disabled (Their presence means true and their absence means false.) If we put an Angular interpolation expression into such an attribute then the binding information would be lost when the browser removes the attribute.