broken checked binding handler behavior when used against array attributes?

The checked binding handler is not working for me against array attributes. Obviously, this code has been in production for ages, so perhaps I'm simply missing something, but I really cannot see how this could possibly be working correctly for others.

Let's walk through the set() for the checked binding handler. This function is called with a jQuery selection of the bound input elements and the incoming attribute value from the model.

      set: function($element, value) {
        if ($element.length > 1) {
          $element = $element.filter('[value="'+ value +'"]');
        }

This is an immediate problem, because value is an array of values here, so we've effectively emptied $element with this statement.

        // Default as loosely-typed boolean:
        var checked = !!value;

Now this check to see if the $element is a radio input will throw an exception because we're attempting to toLowerCase() an undefined value. isRadio() is reproduced below.

        if (this.isRadio($element)) {
          // Radio button: match checked state to radio value.
          checked = (value == $element.val());

Next we check to see if value is an array and then look for $element's value therein. This doesn't work, of course, because $element is empty. Even if it remained a list of jQuery elements, this operation wouldn’t work correctly because jQuery will only return the first selected element’s val() and underscore's contains() is expecting to operate upon a single value.

        } else if (isArray(value)) {
          // Checkbox array: match checked state to checkbox value in array contents.
          checked = _.contains(value, $element.val());
        }

        // Set checked property to element:
        $element.prop('checked', checked);
      },

That $element is still empty, so the checked property cannot be set correctly in any event!

Here is isRadio() for completeness:

      // Is radio button: avoids '.is(":radio");' check for basic Zepto compatibility.
      isRadio: function($element) {
        return $element.attr('type').toLowerCase() === 'radio';
      }
    }),

gmac / backbone.epoxy

broken checked binding handler behavior when used against array attributes? #145