Reacting to comments
In addition to replying to comments from other people, you can also choose to respond with an emoji reaction. The "React" smiley-face icon is located to left of the "Reply" arrow below each comment. If you hover or tap on it, a popover with five reaction emojis will appear.
You can choose an emoji that represents your feelings about the comment; choices include "like", "funny", "wow", "sad", and "disagree."
When a comment has one or more reactions, the total number of reactions will appear on the bottom lefthand side of the comment, along with the top three most popular reactions. Hovering over these emojis will show you a partial list of who selected them. To see all reactions from other commenters, click on any of the emojis, or on the "Reactions" label. You can then view lists of all reactions or per-emoji.
You can view reactions to your comments via the "Activity" tab. Email notifications are currently only available for "like" responses.