I recently read, and very much enjoyed, this author's article on the em-dash: https://themillions.com/2018/01/regarding-the-em-dash.html

(Why yes, it was tempting to use the mark in place of those commas. But I prefer the style of putting spaces around the em-dash, and I fear being downvoted into oblivion by any pedants who strongly adhere to the no-space norms. So commas it is.)