JSFiddle - React, Tailwind, and code Playground
HTML
<html ng-app="demo">
<body ng-controller="ctrl">
<h2>Just demo to check if foo is defined or not.</h2>
<div ng-show="foo || false">
Show this if foo is defined!
</div>
<div ng-show="boo || true">
Show this if boo is undefined!
</div>
</body>
</html>
JavaScript
angular.module("demo", [])
.controller("ctrl", function ($scope) {
$scope.foo = undefined;
$scope.boo = undefined;
});