var app = angular.module('plunker', []);

app.controller('MainCtrl', function($scope) {
  $scope.name = 'World';
});
<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8" />
  <title>AngularJS isDefined() Function - Check if a Value or Reference is Defined inside AngularJS $scope</title>
  <script src="https://code.angularjs.org/1.4.9/angular.js"></script>
  <script>
    var app = angular.module('myApp', []);

    app.controller('myCtrl', ['$scope', function($val) {

      $val.welcomeMsg = function() {
        if (angular.isDefined($val.message)) {
          $val.lblmessage = 'Welcome you  ' + $val.message + '!';
        } else {
          $val.lblmessage = 'Please enter your name';
        }
      }
    }]);
  </script>
</head>

<body ng-app="myApp" ng-controller="myCtrl">
  <h3>
   1:  What is isDefined() Function in AngularJs? <br>
  </h3> Ans : This is use to Check if a Value or Reference is Defined inside AngularJS $scope..
  <br>
  <div>
    <input type="text" ng-model="message" placeholder="Type a message" />
    <button ng-click="welcomeMsg()">Submit</button>
  </div>
  <h1>Result : {{lblmessage}}</h1>
</body>

</html>
/* Put your css in here */