I solved the underlying problem (but not the question itself) with a terminal command instead:

figwheel_notifications(){
  tail -n 1 -F figwheel_server.log | grep --line-buffered "Successfully\|Failed to compile\|Compiler Warning" | while IFS='' read line; do
    if grep --silent Succ <<< $line; then
      terminal-notifier -title 'Figwheel' -message "Successfully recompiled."
    elif grep --silent Warn <<< $line; then
      terminal-notifier -title 'Figwheel' -message "Compilation warning."
    else
      terminal-notifier -title 'Figwheel' -message "Compilation error."
    fi
  done
}