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<html lang="en" ng-app="MyApp">
    <head>
    </head>
    <body ng-controller="AppCtrl">

    <form name="myForm" id="myForm">
     <input type="text" ng-model="field" name="myField" />
        <div ng-show="myForm.myField.$error" style="color: red">
            {{myForm.myField.$error}}
        </div>
    </form>
    <script src="bower_components/angular/angular.js"></script>
    <script src="controller.js"></script>
    </body>
    </html>

angular.module('MyApp',[])
    .controller('AppCtrl', function() {
            var form = document.getElementById("myForm");
            var error = {
                myField: 'Error in this field'
            };
            for (var key in error) {
                form[key].$error = error[key];
            }
    });