The shortcut button will let you open WhatsApp without the need to leave the Facebook app
Facebook is running a trial that features its subsidiary WhatsApp a lot more prominently in the main app .
Myself and Some Android users have reportedly been noticing a dedicated WhatsApp button in the main Facebook app. When clicked, the button acts like a shortcut, opening WhatsApp without the need to leave the Facebook app. This shortcut button has been seen placed in the menu area. If you happen to be one of the users in the control group, it should appear at the top, right under your name. But again, it is a test feature, so most of you will not even see it yet. Also, there is no guarantee if it will even make it as a legitimate feature, it may just die in the testing phase.