knockout.validation.js error in IE8, observable does not support 'extend' property or method

Question

Our knockout validation setup works on FF, Chrome, IE 10 and 9. In IE8 we get the error:

SCRIPT438: Object doesn't support property or method 'extend' knockout.validation.js, line 353 character 17

This is when knockout is trying to add a rule, the observable being passed is a boolean value not a function as it should be. Not sure why a boolean is being passed. We have quite a few constructs like this for e.g.: self.MiddleInitial = ko.observable().extend({ maxLength: 1 });

if we comment out all of the knockout-extends, then we have no error

related html looks like this:

Site is ASP.Net/MVC. versions: knockout 2.2.1.debug, modernizr-2.6.2, jquery 1.10.1, jquery-ui-1.10.3

Thanks in advance.

It seems the error happens when knockout tries to add a "requires" rule on a set of checkboxes. The related observable does not have any validation specified for it.

Answer 1

Maybe your observable is binded to a new HTML5 tag and that makes your observable null?

Or a similar issue to do with you relying on some html5 functionality or feature which fails in IE8?

and obviously null or undefined won't have the method extend.