check null,empty or undefined angularjs

Question

I am creating a project using angularjs.I have variable like

$scope.test = null
$scope.test = undefined
$scope.test = \"\"

I want to check all

Answer 1

if($scope.test == null || $scope.test == undefined || $scope.test == "" ||    $scope.test.lenght == 0){

console.log("test is not defined");
}
else{
console.log("test is defined ",$scope.test); 
}