ProviderEvent

type ProviderEvent: 
  | string
  | (string | string[])[]
  | EventFilter
  | OrphanFilter
  | AccessesFilter;

A ProviderEvent provides the types of events that can be subscribed to on a Provider.

Each provider may include additional possible events it supports, but the most commonly supported are:

"block" - calls the listener with the current block number on each new block.

"error" - calls the listener on each async error that occurs during the event loop, with the error.

"debug" - calls the listener on debug events, which can be used to troubleshoot network errors, provider problems, etc.

transaction hash - calls the listener on each block after the transaction has been mined; generally .once is more appropriate for this event.

Array - calls the listener on each log that matches the filter.

EventFilter - calls the listener with each matching log

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Source

providers/provider.ts:2719