While there's no official tool to hide when you're online, there's a sneaky workaround for the iPhone users.
Wait for a message to arrive on your iPhone so a notification appears in your lock screen. Press down on the notification, and the full text will appear and you can scroll down to see the message in full.
While you will have read the message, it won't trigger the blue ticks or show that you were online, reports Mirror.co.uk.
Currently, WhatsApp's default settings mean your contacts automatically know if you have read their messages and when you were last active on the app.
In privacy settings, you can tap ‘Last Seen' and then Nobody to avoid this, and you can also turn off Read Receipts by pressing the toggle.
At the moment, the only official way not to appear 'online' or 'typing' is to activate Airplane Mode.
This WhatsApp trick works on any device that can upgrade to iOS 13.