ngMinlength adds the minlength 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 minlength error key if the ngModel.$viewValue
is shorter than the integer obtained by evaluating the Angular expression given in the
ngMinlength attribute value.
minlength attribute is used, with two
differences:
ngMinlength does not set the minlength attribute and therefore HTML5 constraint
    validation is not available.
  ngMinlength value must be an expression, while the minlength value must be
    interpolated.
  <ANY>
...
</ANY>
      
<script>
  angular.module('ngMinlengthExample', [])
    .controller('ExampleController', ['$scope', function($scope) {
      $scope.minlength = 3;
    }]);
</script>
<div ng-controller="ExampleController">
  <form name="form">
    <label for="minlength">Set a minlength: </label>
    <input type="number" ng-model="minlength" id="minlength" />
    <br>
    <label for="input">This input is restricted by the current minlength: </label>
    <input type="text" ng-model="model" id="input" name="input" ng-minlength="minlength" /><br>
    <hr>
    input valid? = <code>{{form.input.$valid}}</code><br>
    model = <code>{{model}}</code>
  </form>
</div>