Not to mention how inconvenient it is to actually add emoji. Chances are that the person who wrote that page didn't draft it from a phone with an easily accessible emoji keyboard, nor from a physical keyboard with emoji bindings. So they'd have to go out of their way to open up an on-screen emoji keyboard, or an emoji webpage, and paste those emojis one by one.
I agree though, use of emoji outside talking to your friend, to me, is an instant warning of immaturity, and a flag of more to come.
The OP post was horrendous to look at, I'm not sure why anyone thought that it would help with understanding the content.
On the flip side, I would never allow that code to be used in any of my projects, nor would I want to work with any contributors that think it is a "good" practice (nevermind "best"). To my mind, this documentation screams "unprofessional". I would be embarrassed to show it to any of my customers.
The code is not be the only thing by which a project should be judged. Bad documentation is worse than no documentation, because the author had a choice about the format and style that will be used. This project chose... poorly.
What the hell is professionality? Wikipedia says something along the lines of "standards of education and training that prepare members of the profession with the particular knowledge and skills necessary to perform their specific role within that profession".
A (considerate) use of emojis, images and jokes (basically: anything that isn't dry text) can work wonders to make a document more digestible, leading to more effective transfer of information and increased enthusiasm for your brand. I would consider that doing your job quite effectively.
Totally depends on the target audience, of course. I have experienced instances of "over-doing it" before (this is one of them), so I do empathize with the more boring people of the industry a little. But not overly much. "No fun allowed" mentalities can massively hurt morale (remember: this costs money), in my opinion.
"Feeling emojis" are great because they emulate non-verbal communication. A smile is a smile, a thumbs up is a "hm" or "okay". Text communication is by nature asynchronous so we have to find ways to cope with that. On the other hand, documentation doesn't need non-verbal communication.
Of course, some emojis can be used for both verbal and non-verbal communication. But stuff like burger? Or cashier? I don't see the point.
Another thing: this is possibly the worst explanation about concurrency and async/await I've ever read.
EDIT: HN doesn't seem to support emojis. Changed to a markdown like format instead.