What is topics?

Questions
1

What is topics? I understood is used to filter the received response from websocket, it that right?

  • topics [optional] - Array of 32 Bytes DATA topics.

Topics are order-dependent. A note on specifying topic filters: Topics are order-dependent. A transaction with a log with topics [A, B] will be matched by the following topic filters:

  • [] - anything"
  • [A] - A in first position (and anything after)
  • [null, B] - anything in first position AND B in second position (and anything after)
  • [A, B] - A in first position AND B in second position (and anything after)"
  • [[A, B], [A, B]] - (A OR B) in first position AND (A OR B) in second position (and anything after)
2

Correct it is used to filter the Ethereum events from new blocks to only the ones your app cares about. This is a good primer that explains it: https://codeburst.io/deep-dive-into-ethereum-logs-a8d2047c7371