Keep track of vertical scrolling in your html files.
Dispatch a custom event when an offset threshold is reached.
Display the scroll status in the UI (conditionally).
All functionality is implemented with plain JavaScript, HTML and CSS.
handleScroll is the function handling the scroll event and creating a new event (scrollProgress) that is dispatched to window when the vertical offset reaches a certain threshold.
listenToProgress is the function called by the custom event listener, which logs the event.detail to the console (or can alert the user)
handleProgressInUI is a function (called conditionally) used to display information about the scroll status in the document.
generateText is just a function used to populate the demo html file with enough text content to enable vertical scroll.
Clone the repo and open the index.html file in a browser with JS enabled.