Before you get downvoted, I'll give you an idea of how to do it
Recording visitors is in the realm of analytics, of which Google Analytics is the most popular & recognized
Analytics
Analytics systems work with 3 parts:
- Capture
- Processing
- Display
The process of capturing & processing data is fundamentally the same -- put a JS widget on your site to send a query to the server with attached user data. Processing the data puts it into your database
Displaying The Data
The difference for many people is the display of the data they capture
- Google Analytics displays the data in their dashboard
- Ebay displays the data as
x people bought in the past hour
- You want to show the number of people viewing an item
The way to do this is to hard-code the processing aspect of the data into your app
I can't explain the exact way to do this, because it's highly dependent on your stack, but this is the general way to do it