Event Trigger

Watch Now: Learn more by watching our video Web3 Function Triggers, available on YouTube.

Event Context

For event triggered typescript functions, use the Web3FunctionEventContext instead of the regular Web3FunctionContext on your onRun handler. The context will then include a log property containing your full event log that you can parse and process.

Event Triggered Typescript Function example

import { Interface } from "@ethersproject/abi";
import { Web3Function, Web3FunctionEventContext } from "@gelatonetwork/web3-functions-sdk";

const NFT_ABI = [
  "event Transfer(address indexed from, address indexed to, uint256 indexed tokenId)",

Web3Function.onRun(async (context: Web3FunctionEventContext) => {
  // Get event log from Web3FunctionEventContext
  const { log } = context;
  // Parse your event from ABI
  const nft = new Interface(NFT_ABI);
  const event = nft.parseLog(log);

  // Handle event data
  const { from, to, tokenId } = event.args;
  console.log(`Transfer of NFT #${tokenId} from ${from} to ${to} detected`);
  return { canExec: false, message: `Event processed ${log.transactionHash}` };

Testing locally

To test your event triggered typescript function, you can add a log.json file in your web3 function directory:

Copy in the log.json file the raw data of the event you want to test:

  "blockNumber": 48758053,
  "blockHash": "0x6794a56583329794f184d50862019ecf7b6d8ba6b3210f68ca4b91a8fa81817d",
  "transactionIndex": 29,
  "removed": false,
  "address": "0xb74de3F91e04d0920ff26Ac28956272E8d67404D",
  "data": "0x",
  "topics": [
  "transactionHash": "0x2c500a55f5c24d587e73805975d91395634a971dca5939f43d34d774d0f7147b",
  "logIndex": 343

The data in log.json will be injected in your event context in local runs via CLI:

npx w3f test event/index.ts --logs
Web3Function running logs:
> Transfer of NFT #4249 from 0x0000000000000000000000000000000000000000 to 0xeeC2ba9B9F0202c63bba29Ea9A4Ce5c23f9865FD detected

Web3Function Result:
 ✓ Return value: {"canExec":false,"message":"Event processed 0x2c500a55f5c24d587e73805975d91395634a971

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