This looks interesting, but I wish there was an explanation of how it works; I'm particularly curious about how it extracts repeated substrings. I tried reading the code, but it starts off with:

  let X, B, O, m, i, c, e, N, M, o, t, j, x, R;

and doesn't get any more readable from there. (And that's the unminified version!)

There aren't any tests, either, so if you're using this and find a bug I guess you just have to hope that nothing breaks when you change a line like

  for(M=N=e=c=0,i=Q.length;!c&&--i;)!~s.indexOf(Q[i])&&(c=Q[i]);