How to spy on WhatsApp conversations?

Jealous partners use spyware to spy on WhatsApp conversations. With it, they can find out people involved in the conversations, their contact details and phone numbers, and exact date of communication. This kind of information is attractive due to its insightfulness. How does it track WhatsApp?
Spyware has to be set up on a device. It is invisible. When the phone’s owner texts on WhatsApp to someone else, spyware records it immediately. A user logs in to an online account created for them during the registration and views WhatsApp chats. The necessary condition to spy on WhatsApp is the target phone’s connection to the Internet.