Using the event dispatch mechanism is flat-out bigger, anyway. Here’s the interface of the original script (that is, global pub/sub functions taking a name), except that the receiver site no longer needs to look at the .detail property so it’s better:

  let t={};
  sub=(e,c)=>((e=t[e]??=new Set).add(c),()=>e.delete(c));
  pub=(n,d)=>t[n]?.forEach(f=>f(d))

The original was 149 bytes; this is 97.

(The nullish coalescing assignment operator ??= has been supported across the board for 4½ years. Avoiding it will cost six more bytes.)