Angularjs check defined variable

<!DOCTYPE html>
<html lang="en">
<head>
 <script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.2.13/angular.min.js"></script>
 <script>
var myApp = angular.module("myApp", []);
 myApp.controller("myController", function($scope) {
  var a;
  var b = 10;
  $scope.result1 = '';
  $scope.result2 = '';
  $scope.chackDefinedVars = function() {
    if(angular.isDefined(a)){
		$scope.result1 = true;
	}else{
		$scope.result1 = false;
  }
  if(angular.isDefined(b)){
		$scope.result2 = true;
	}else{
		$scope.result2 = false;
  }
  }
});
</script>
</head>
<body>  
<div ng-app="myApp">  
<div ng-controller="myController">  
    <button ng-click ="chackDefinedVars()" >Check Vars</button>
	<br>
	Result for a = {{result1}}<br>
	Result for b = {{result2}}
</div> 
</div>
</body>  
</html>