The code is a bit dense for my taste, these are extracts from the unminified version:

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

RegExp(`${(g[2]?g[2]:'')+g[0]}|${(g[3]?g[3]:'')+g[1]}`,'g');