SubscriptionType:
    | "newHeads"
    | "logs"
    | "newPendingTransactions"
    | "syncing"

The type of subscription to create. Must be one of the following:

  1. newHeads - New block headers.
  2. logs - Logs matching a filter object.
  3. newPendingTransactions - New pending transactions.
  4. syncing - Changes in syncing status.