No idea what you are talking about. $@MID@$ is used in the database files to indicate the start of a new message. It is not used on any elog web page. If you want to put the message ID on your web page, you should use the variable "$message id" as written in the documentation. You say JS, where is your JS running? You wrote a JS program to work on the raw elog database files? Or you wrote an extension to run in your browse? You have to be a bit clearer.
I tried using this $@MID@$ in JS as a variable and cannot doit. I researched a little and found no answer on special character usage. If anyone knows, please lemme know. I also tried breifly in Elogd to change it to something like just MID, but need a better editor as (Kate) is not saving the program back in correct iso (character) format. So I thought I'd pose the question in the meanwhile.