On Mar 23, 2017, Facebook added reactions to Messenger, the same feature has now extended to comments. Because why bother commenting on a comment when you can just click the “Heart” emoji?
Unlike the implementation of posts and Messenger, the emoji seem to crowd and overlap a bit especially as more reactions are added. To add a reaction, just hover over the Like button and see your default options of six. Unlike the Messenger’s mobile implementation, there is no animation after you click a reaction button.
It is a great feature as you don't have to type and you can just directly show your emotions and reactions through these emojis. This feature had also rolled on to the desktop version of Facebook, so if you didn’t see it yet, you will soon.