code: function isConnected(remote) {
    if (isNaN(remote._ledger_current_index)) {
      // Remote is missing the index of last ledger closed. Unprepared to submit
      // transactions
      return false;
    }
  
    var server = remote.getServer();
    if (!server) {
      return false;
    }
  
    if (remote._stand_alone) {
      // If rippled is in standalone mode we can assume there will not be a
      // ledger close within 30 seconds.
      return true;
    }
  
    return (Date.now() - server._lastLedgerClose) <= CONNECTION_TIMEOUT;
  }
docs: Determine if remote is connected based on time of last ledger closed
  
  @param {Server} server
  @return {Boolean}