query past event info from previous substrate blocks

query-substrate-block-data.js

// using polkadot.js api this code will retrieve events from blocks 0-50
// you can go as far back on full archive nodes and about 150-200 blocks
// back on non-archive nodes
// code contributed from Stefie@riot https://github.com/polkadot-js/api/issues/578

for(i=50;i>=0;i--){
    var hash = await api.rpc.chain.getBlockHash(i); 
    var events = await api.query.system.events.at(hash);
    console.log(`\n #${i} Received ${events.length} events:`);

    // loop through the Vec<EventRecord>
    events.forEach((record) => {
        // extract the phase, event and the event types
        const { event, phase } = record;
        const types = event.typeDef;

        // show what we are busy with
        console.log(`\t${event.section}:${event.method}:: (phase=${phase.toString()})`);
        console.log(`\t\t${event.meta.documentation.toString()}`);

        // loop through each of the parameters, displaying the type and data
        event.data.forEach((data, index) => {
        console.log(`\t\t\t${types[index].type}: ${data.toString()}`);
        });
    });
 }