web3: How do I get past events of myContract.myEvent?

Question

I use the following JS code to get notified of Solidity events and it works well for incoming new events:

myContract.myEvent().watch((error, result) => {
  if (error)
    console.log('Error in myEvent event handler: ' + error);
  else
    console.log('myEvent: ' + JSON.stringify(result.args));
});

I would like to use the same code for initializing the JS app on startup. e.g. I start the JS app on block 100 but there were already some events fired at block 20 and 30. These two past events are not being processed with the code above. As alternatives, I also tried via

myContract.myEvent((error, result) => {

and

myContract.myEvent({fromBlock: 0, toBlock: 'latest'}, (error, result) => {

Still these two options don't give me past events.

Answer 1

I finally figured out how to properly use .get() mentioned in the answer by Roland:

myContract.myEvent({}, { fromBlock: 0, toBlock: 'latest' }).get((error, eventResult) => {
  if (error)
    console.log('Error in myEvent event handler: ' + error);
  else
    console.log('myEvent: ' + JSON.stringify(eventResult.args));
});

Worth mentioning that the eventResult object is an array containing one entry per event call:

[{
    "address": "0x80d346f14eb1bb47bc112b066f74ceb5e0a07c78",
    "blockNumber": 180173,
    "transactionIndex": 1,
    "transactionHash": "0x2c34b00a9b137a506afc6b80ccf159858415c48f403d357c35e509a03fe4c8bc",
    "blockHash": "0xc737758878120a70ed5f9d4fb412fc05231fbe5473e87e6f2194361537b85a4f",
    "logIndex": 2,
    "removed": false,
    "event": "myEvent",
    "args": {
        "id": "1"
    }
}, {
    "address": "0x80d346f14eb1bb47bc112b066f74ceb5e0a07c78",
    "blockNumber": 180179,
    "transactionIndex": 1,
    "transactionHash": "0x6372cc429ffe28c717f7e26c100da2e7395bd23ac466da20643299dfe57ed380",
    "blockHash": "0xcc6c13043ceeab8a3c5dbf4f4937b7e3d02c614256615cb8c3b63fdcb46f0d0a",
    "logIndex": 2,
    "removed": false,
    "event": "myEvent",
    "args": {
        "id": "2"
    }
}]

Answer 2

Instead of .watch() use .get(). Can be lagging a bit, because events are not saved in the state-trie, behind the curtain it will scan all blocks, therefore you might give it a fromBlock

fromBlock: Number|String - The number of the earliest block (latest may be given to mean the most recent and pending currently mining, block). By default latest.

https://github.com/ethereum/wiki/wiki/JavaScript-API#parameters-29

Answer 3

With web3.js version 1.0 there are two more ways to get past events:

• subscribe('logs'), with the option `fromBlock: '0x0'.
• getPastLogs().

The first option keeps on listening for new events. If you are just looking for all past events, getPastLogs is sufficient.

Answer 4

If you get an array of objects as your result:

[object Object],[object Object],[object Object],[object Object],[object Object]...

then you need to extract the key value pair of "args" inside the objects:

    var event1;
    for(var i = 0; i < result.length ; i++){
      event1 = JSON.stringify(result[i].args);
      document.getElementById("TxAllEvents").innerHTML += event1;
    }

Answer 5

Works on web3.js@1.0.0-beta.34:

  MyContract.events.MyEvent({}, { fromBlock: 0, toBlock: 'latest' }).on(
    'data', function(event) {
    console.log(event);
  }).on('error', console.error);