NgModel needs a way to manually re-run the formatter chain

[jpsimons]

See this fiddle:
http://jsfiddle.net/tPWBK/1/

Say you have a data transformation directive that requires 'ngModel' and adds to the formatter and parser chains. If the transformation is dependent on some dynamic data other than $modelValue or $viewValue, there's no way to do a watch on that data and re-run the formatter chain.

See this excerpt from https://github.com/angular/angular.js/blob/master/src/ng/directive/input.js#L1081

$scope.$watch(function ngModelWatch() {
  var value = ngModelGet($scope);

  // if scope model value and ngModel value are out of sync
  if (ctrl.$modelValue !== value) {

    var formatters = ctrl.$formatters,
        idx = formatters.length;

    ctrl.$modelValue = value;
    while(idx--) {
      value = formatters[idx](value);
    }

    if (ctrl.$viewValue !== value) {
      ctrl.$viewValue = value;
      ctrl.$render();
    }
  }
});

Should everything inside the (ctrl.$modelValue !== value) check be a function that's exposed publicly on NgModelController?

[jpsimons]

Well, I guess one could just copy that block into a directive. It's all public stuff. Would be handy to have a function to do it for you though.