ngMaxlength adds the maxlength validator to ngModel.
It is most often used for text-based input controls, but can also be applied to custom text-based controls.
The validator sets the maxlength error key if the ngModel.$viewValue
is longer than the integer obtained by evaluating the Angular expression given in the
ngMaxlength attribute value.
maxlength attribute is used, with two
differences:
ngMaxlength does not set the maxlength attribute and therefore HTML5 constraint
    validation is not available.
  ngMaxlength attribute must be an expression, while the maxlength value must be
    interpolated.
  <ANY>
...
</ANY>
      
<script>
  angular.module('ngMaxlengthExample', [])
    .controller('ExampleController', ['$scope', function($scope) {
      $scope.maxlength = 5;
    }]);
</script>
<div ng-controller="ExampleController">
  <form name="form">
    <label for="maxlength">Set a maxlength: </label>
    <input type="number" ng-model="maxlength" id="maxlength" />
    <br>
    <label for="input">This input is restricted by the current maxlength: </label>
    <input type="text" ng-model="model" id="input" name="input" ng-maxlength="maxlength" /><br>
    <hr>
    input valid? = <code>{{form.input.$valid}}</code><br>
    model = <code>{{model}}</code>
  </form>
</div>