Setting model to NaN causes infdig if $asyncValidators is used

[tomyam1]

An infinite digest error is thrown when a model is set to NaN and there is an asynchronous validator.

Please check plunker at http://plnkr.co/edit/u9Sq12?p=preview.
When we set model to a string or to null - everything works as expected.
When we set model to NaN there is an infdig error:

Error: [$rootScope:infdig] 10 $digest() iterations reached. Aborting!
Watchers fired in the last 5 iterations: []
http://errors.angularjs.org/1.3.14/$rootScope/infdig?p0=10&p1=%5B%5D
    at angular.js:63
    at Scope.$digest (angular.js:14281)
    at Scope.$apply (angular.js:14506)
    at HTMLButtonElement.<anonymous> (angular.js:21443)
    at HTMLButtonElement.eventHandler (angular.js:3014)
angular.js:63 Uncaught Error: [$rootScope:infdig] 10 $digest() iterations reached. Aborting!
Watchers fired in the last 5 iterations: []
http://errors.angularjs.org/1.3.14/$rootScope/infdig?p0=10&p1=%5B%5D

This happens because ngModelWatch checks that modelValue !== ctrl.$modelValue, which is true for NaN.

Thus, when we set the model to NaN, $$runValidators is called in every digest cycle. If we have an async validator, it causes a push to asyncQueue and so another cycle is needed.

ngModelWatch returns modelValue, which is NaN so the watch is not considered dirty because $digest() treats NaN as equal to NaN.

I think a good solution would be to treat NaN as equal to NaN in ngModelWatch
Edit:
Check http://plnkr.co/edit/aZZmyP?p=preview
ngModelWatch is changed to

if (modelValue !== ctrl.$modelValue &&
      !(typeof modelValue === 'number' && typeof ctrl.$modelValue === 'number' && isNaN(modelValue) && isNaN(ctrl.$modelValue))) {
      ctrl.$modelValue = ctrl.$$rawModelValue = modelValue;

and this indeed solved the infdig

[zhongsp]

In ngModelWatch , we could update to modelValue and ctrl.$modelValue are not equal, and any of both is not NaN.

    // if (modelValue !== ctrl.$modelValue)
    if (modelValue !== ctrl.$modelValue && 
        (modelValue === modelValue || ctrl.$modelValue === ctrl.$modelValue)) {

[wesleycho]

It would be better to do

if (modelValue !== ctrl.$modelValue &&
  equals(modelValue, modelValue) || equals(ctrl.$modelValue, ctrl.$modelValue)) {
...
}

I think - angular.equals already has a check for NaN, so it would screen out this case and do a more proper check.

[gkalpak]

I don't think using the (potentially expensive) equals in a rather critical path is a good idea.
@zhongsp's suggestion seems fine though.

[Narretz]

I opened #11411 for your consideration. equals is too expensive, but @zhongsp solution works.