Example for stackoverflow.

by Stepan Kasyanenko

HTML

<script src="https://cdn.rawgit.com/Stepan-Kasyanenko/use-form-error/master/src/use-form-error.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.4.9/angular-messages.min.js"></script>
<div ng-app="ExampleApp">
  <div ng-controller="ExampleController">

    <div ng-form="testForm" use-form-error="sumNot100" use-error-expression="input_1+input_2+input_3!=100">
      <label>Sum of all input must be 100</label>
      <br>
      <label>Input 1</label>
      <input ng-model="input_1" type="number" name="input_1">
      <label>Input 2</label>
     <input ng-model="input_2" type="number" name="input_2">
     <label>Input 3</label>
     <input ng-model="input_3" type="number" name="input_3">
      <div ng-messages="testForm.$error" class="errors">
        <div ng-message="sumNot100">
          Sum of all input not equal 100
        </div>
      </div>
      <button ng-disabled="testForm.$invalid">
        Submit
      </button>

    </div>
  </div>
</div>

CSS

.errors {
  color: maroon
}

.success {
  color: green;
}

JavaScript

angular.module('ExampleApp', ['use', 'ngMessages'])
  .controller('ExampleController', function($scope) {

  });