Update number boundary using ng-model

Question

I'm trying to bound an input number using ng-model. If the input number is out of the range it will show a popup hint.

<input type="number" class="input-number" id="bar-length" value="" ng-model="barLength" min="300" max="650" required>
<div class="input-help">
    <h4>The length is outside the current range of acceptable values.</h4>
</div>

In CSS it is:

/* Help should show when invalid */
.ng-invalid + .input-help {
    display: block;
}

The validation works quite well. However, I want to change the bound range when the units changes from "mm" to "in", so I wrote in Javascript with JQuery:

if (units === "in") {
    $("#bar-length").attr("min", 15.75);
    $("#bar-length").attr("max", 31.50);
}

It seems that the ng-model boundary does not change accordingly. The popup hint still comes up when the input number is within 15.75 and 31.50. I'm new to this and I got no idea about how to fix it. What should I do?

Answer 1

Don't use jquery unless you wrap it in directives, think in the angularJS mindset, As I pointed out in comments, this is not natively suppoted by angular yet, but you can write directives to make it work:

http://jsfiddle.net/g/s5gKC/3/

var app = angular.module('app', []);

function isEmpty(value) {
  return angular.isUndefined(value) || value === '' || value === null || value !== value;
}

app.directive('ngMin', function() {
    return {
        restrict: 'A',
        require: 'ngModel',
        link: function(scope, elem, attr, ctrl) {
            scope.$watch(attr.ngMin, function(){
                ctrl.$setViewValue(ctrl.$viewValue);
            });
            var minValidator = function(value) {
              var min = scope.$eval(attr.ngMin) || 0;
              if (!isEmpty(value) && value < min) {
                ctrl.$setValidity('ngMin', false);
                return undefined;
              } else {
                ctrl.$setValidity('ngMin', true);
                return value;
              }
            };

            ctrl.$parsers.push(minValidator);
            ctrl.$formatters.push(minValidator);
        }
    };
});

app.directive('ngMax', function() {
    return {
        restrict: 'A',
        require: 'ngModel',
        link: function(scope, elem, attr, ctrl) {
            scope.$watch(attr.ngMax, function(){
                ctrl.$setViewValue(ctrl.$viewValue);
            });
            var maxValidator = function(value) {
              var max = scope.$eval(attr.ngMax) || Infinity;
              if (!isEmpty(value) && value > max) {
                ctrl.$setValidity('ngMax', false);
                return undefined;
              } else {
                ctrl.$setValidity('ngMax', true);
                return value;
              }
            };

            ctrl.$parsers.push(maxValidator);
            ctrl.$formatters.push(maxValidator);
        }
    };
});

angular.bootstrap(document.body, ['app']);

Edit: refresh validation state when contraint change