I would say that's not a great example. I wrote literally that function as a utility in my project, and it was honestly kind of tricky. There's a big gap between knowing how to use a Promise, which is necessary and closer to an "idea what a Promise is", vs how to build one from scratch, which is nice but probably not necessary for a generic frontend job. It wasn't even really necessary for me, I just wanted to be able to pause functions with an await statement.