So if you wanna make web app notification I suggest you to use Push.js or SoneSignal framework for Web/mobile app.
You will have to use Socket.io and some backend framework, I will user Express for this example.
|node.js/express||Simple backe-end framework for Node.js application, very easy to use and extremely powerful|
|Socket.io||Socket.IO enables real-time bidirectional event-based communication. It works on every platform, browser or device, focusing equally on reliability and speed.|
|Push.js||The world's most versatile desktop notifications framework|
|OneSignal||Just another form off push notifications for Apple devices|
|Firebase||Firebase is Google's mobile platform that helps you quickly develop high-quality apps and grow your business.|