How to get events emitted by a transaction with web3.js

Question

I'm writing a user interface in Javascript and I'm using the web3.js library.

I have the transaction hash of a confirmed transaction. I would like to get an array of all events emitted by that transaction.

I don't necessarily need all events, just the ones emitted by my smart contract by the execution of that transaction.

Can this be done using web3.js? What's a good way to accomplish this?

See also: https://ethereum.stackexchange.com/questions/16313/how-can-i-view-event-logs-for-an-ethereum-contract — Onshop, Mar 10 '21 at 19:33

score 10 · Answer 1 · answered Oct 30 '19 at 19:22

If you're using Web3 v1 then you can use web3.eth.getTransactionReceipt(tx). It returns logs property as a part of a result.

You can categorize events by looking at their topics property.

Sample getTransactionReceipt result:

{
    "transactionHash": "0x7e2e90d913246933b30049c568d9a9768eca5be6fed331656458c2a479f30908",
    "transactionIndex": 0,
    "blockHash": "0x2af7bb564cc6a4155895b3238d5a0f227ecae2bfc5e65d24be5066f7a0e1b035",
    "blockNumber": 127,
    "from": "0x9442ed348b161af888e6cb999951ae8b961f7b4b",
    "to": "0xf1365f7f85c20885cab2472d36c59861bcfbd071",
    "gasUsed": 298630,
    "cumulativeGasUsed": 298630,
    "contractAddress": null,
    "logs": [
        {
            "logIndex": 0,
            "transactionIndex": 0,
            "transactionHash": "0x7e2e90d913246933b30049c568d9a9768eca5be6fed331656458c2a479f30908",
            "blockHash": "0x2af7bb564cc6a4155895b3238d5a0f227ecae2bfc5e65d24be5066f7a0e1b035",
            "blockNumber": 127,
            "address": "0xF1365F7F85C20885caB2472d36c59861BCfbD071",
            "data": "0x",
            "topics": [
                "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
                "0x0000000000000000000000000000000000000000000000000000000000000000",
                "0x0000000000000000000000005b1b89a48c1fb9b6ef7fb77c453f2aaf4b156d45",
                "0x0000000000000000000000000000000000000000000000000000000000000000"
            ],
            "type": "mined",
            "id": "log_3b3793c3"
        },
        {
            "logIndex": 1,
            "transactionIndex": 0,
            "transactionHash": "0x7e2e90d913246933b30049c568d9a9768eca5be6fed331656458c2a479f30908",
            "blockHash": "0x2af7bb564cc6a4155895b3238d5a0f227ecae2bfc5e65d24be5066f7a0e1b035",
            "blockNumber": 127,
            "address": "0xF1365F7F85C20885caB2472d36c59861BCfbD071",
            "data": "0x00000000000000000000000000000000000000000000000000000000000dbba00000000000000000000000005b1b89a48c1fb9b6ef7fb77c453f2aaf4b156d45",
            "topics": [
                "0xc0300f89fa66c737609c90575f912c101a539bdc6659f1562ba9b0868f8d181d",
                "0x0000000000000000000000000000000000000000000000000000000000000000"
            ],
            "type": "mined",
            "id": "log_f5493494"
        }
    ],
    "status": true,
    "logsBloom": "0x00000000000000000000000000000100000000000000000000000000000000002000000000000000000000000000000000000000000000040000000000000000000000000000000000800008000008000000000000000000000000000000000000000000020000000000000000000800000000000000000000400010000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002000002000000000000000000020000000000200000000000000000000020000000000000000000000000000000000000000000000000000000000000000000",
    "v": "0x2dc32acb6eb",
    "r": "0xc61fe8837727dda287ab1253006832ca7546a191580dd2e3d676f5e77bdd3c9f",
    "s": "0x6db737b383a9cfd5f59bc41351adf0665fea86b6708c123f7103413d43972859"
}

score 2 · Answer 2 · answered Jan 31 '19 at 14:48

This is a bit convoluted since Web3 does not directly expose events emitted by a transaction, but it can be queried by tracing the transaction.

Trace transaction : https://github.com/ethereum/go-ethereum/wiki/Management-APIs#debug_tracetransaction
It will return a block of info for each instruction of transaction. (PUSH1 in this example)

{ depth: 1, error: "", gas: 162106, gasCost: 3, memory: null, op: "PUSH1", pc: 0, stack: [], storage: {} }

Filter for opcodes LOG0 -- LOG4. These instructions are used for raising events.

Decode Event name from the data that is part of OPCODE block

This seems to contradict the answer from Daniel Kmak, which clearly shows the logs available in the transaction receipt. — Adam Spiers, Jul 15 '21 at 09:45

score 1 · Answer 3 · answered Jan 31 '19 at 14:19

So far, I've solved this in a slightly dirty way:

Use getTransaction(txhash) to get the block number in which the transaction was confirmed.
Use getPastEvents("allEvents", {fromBlock: blockNumber, toBlock: blockNumber}) to get all events emitted by my contract in that block
Filter out the events with the correct txhash

I would prefer not to fetch and loop over all events in a block just to get the ones emitted by one transaction, so I'm not going to accept my own answer.

Onshop · Answer 4 · 2021-03-10T19:32:57.120

This worked for me with a contract instance 'remittance' calling the 'release' function emitting an event called 'HashCreated':

await remittance.release(passBytes32, {from: broker});
remittance.getPastEvents('HashCreated', {}, function(error, events){ 
        console.log(events); })
    .then(function(events){
        console.log(events)
    });

Derived from and credit to Zack McGinnis https://ethereum.stackexchange.com/a/45403/48189

How to get events emitted by a transaction with web3.js

4 Answers4