fix(NgModel): use string representation of the value in the ngMinlength and ngMaxlength

Fixes angular#7848

Author: airato

src/ng/directive/input.js

@@ -2189,7 +2189,7 @@ var maxlengthDirective = function() {
         ctrl.$validate();
       });
       ctrl.$validators.maxlength = function(value) {
-        return ctrl.$isEmpty(value) || value.length <= maxlength;
+        return ctrl.$isEmpty(value) || value.toString().length <= maxlength;
       };
     }
   };
@@ -2207,7 +2207,7 @@ var minlengthDirective = function() {
         ctrl.$validate();
       });
       ctrl.$validators.minlength = function(value) {
-        return ctrl.$isEmpty(value) || value.length >= minlength;
+        return ctrl.$isEmpty(value) || value.toString().length >= minlength;
       };
     }
   };

test/ng/directive/inputSpec.js

@@ -1400,6 +1400,11 @@ describe('input', function() {
 
       changeInputValueTo('aaa');
       expect(inputElm).toBeValid();
+
+      scope.$apply(function() {
+        scope.value = 1234;
+      });
+      expect(inputElm).toBeValid();
     });
 
     it('should listen on ng-minlength when minlength is observed', function() {
@@ -1446,6 +1451,11 @@ describe('input', function() {
 
       changeInputValueTo('aaa');
       expect(inputElm).toBeValid();
+
+      scope.$apply(function() {
+        scope.value = 42;
+      });
+      expect(inputElm).toBeValid();
     });
 
     it('should listen on ng-maxlength when maxlength is observed', function() {