GET PREVIOUS EVENTS ON POLKADOT CHAIN

old_events.js

const oldEvents = async () => {
    // get current block 
    const currentBlock = await api.rpc.chain.getHeader();
    const currentBlockData = currentBlock.toJSON();
    // By default a Polkadot/Substrate node will only keep state for the last 256 blocks, unless it is explicitly run in archive mode
    for (let index = 0; index < 255; index++) {
    const blockNum = currentBlockData.number - (index + 1);
    const blockHash = await api.rpc.chain.getBlockHash(blockNum);
    const apiAt = await api.at(blockHash.toJSON());
    const events = await apiAt.query.system.events();
    events.forEach((record) => {
      // Extract the phase, event and the event types
      const { event } = record;
      const { method } = event.toHuman();
      // logs the event name 
      console.log({method})
    });
  }
}