Type Inference for decodeEventLog not inferring the correct value

[mulfdev]

I have this bit of code spitting out all of the logs for a given ERC20 contract. Based on the docs for decodeEventLog, I should get a return type that looks like this:

/**
 *  {
 *    eventName: 'Transfer',
 *    args: {
 *      from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
 *      to: '0x70997970c51812dc3a010c7d01b50e0d17dc79c8'
 *      value: 1n
 *    }
 *  }
 */

However, what I actually get is

This causes the required type assertion in the included code. After debugging a bit I could not get anything other than the empty object as the inferred type. Any help would be wonderful. Package version 0.3.2

import { createPublicClient, decodeEventLog, http, parseAbiItem } from "viem";
import { mainnet } from "viem/chains";
import { erc20ABI } from "@wagmi/core";

type TransferLogArgs = {
  from: string;
  to: string;
  value: BigInt;
};

const transport = http(
  "https://eth-mainnet.g.alchemy.com/v2/my-correct-api-key"
);

const client = createPublicClient({
  chain: mainnet,
  transport,
});

async function main() {
  const BLOCK_INTERVAL = 250;
  let startBlock = 15390081;


  setInterval(async () => {
    console.log({ startBlock });
    const changes = await client.getLogs({
      address: "0xb24cd494faE4C180A89975F1328Eab2a7D5d8f11",
      event: parseAbiItem(
        "event Transfer(address indexed from, address indexed to, uint256 value)"
      ),
      fromBlock: BigInt(startBlock),
      toBlock: BigInt(startBlock + BLOCK_INTERVAL),
    });

    startBlock += BLOCK_INTERVAL;

    for (const change of changes) {
      const log = decodeEventLog({
        abi: erc20ABI,
        data: change.data,
        topics: change.topics,
        eventName: change.eventName,
      });

      if (typeof log.args === "undefined") {
        return new Error("incorrect data");
      }
  
      const info = log.args as TransferLogArgs;

      console.log(info);
    }
  }, 1500);
}

main().catch((err) => {
  console.log(err);
  process.exit(1);
});

[jxom]

Looks like a type bug. We can have a look into it! For the meantime, you may want to cast your topics to [Hex, Hex, Hex] (the expected number of topics for the log) to get the type inference to work. See line 36:

https://www.typescriptlang.org/play?#code/JYWwDg9gTgLgBAbzgYygUwIYzQBQK4BGANsMgMIloB2MANHACZrIRMCiAbtTADIQDm9ABYwYYemAxQAzmgCCBYAElsIegAk0ADzgBfOADMoEEHABEHYGhBmA3AFgAUKEixEcEBmBUqaePqMTc0trAHpkIS8qaTsnF2h4JDQoZAAmAAY5ACElPUNjUzMAAQB3DH4QYHDoNFjHJxZo+BgoDGjXeABeOBExAAonOHNesGkALlDQvyEAWk9vXxgAOn4ljCII6wBPJZYQUI5U0JAtmZYodGQYGYwwYBmAazQtsycASgd6x0bpeGRKGhwbqoTDYfDEUgUKw0PoIQYoSLeMYeKKLWjwlptaQddGOXQfJxODDSLZUZCGPBkmDACBUFHePpvRDwn7wLI8ADyZAA0gB9JQAOQAKmwAEoANTkPCBcFSAFZ0p8hkQ-HBflIYFkiBBkA8ZQBGOUAZgAnOl0gAOfWfQmOIayGBKGjJDjrPrE0nkxlAgB8zLtQxQtOkEBVS21-FhapgGq1Or1+KVgdZCLa-DQ0hlGDKwD+AOW6d4AmksPhgbgGAYDHQ0nG5nSWgIqQALMgGM2Tc2DBg2M2yPqLZkLSaTQB2OUAMX1RtSFrYGCbGFHABE5QwLQZ9fqzLjy0M0FwaMjJDJ5IoVNYBgG9+YD9w4ELWtEDMl3VWa5nvEwtGgGPkTPQlbVhmn5UN+v5wDAED0Hg3gwPKABscCukQeBoG8rzXoGby7nugQgHGurIlkwD8E6MB9OqsCEQ8OFloGUE0cRpHkZRMbUdqupwAA1HA7JcnygoihKUp0Vhia2uWVGapxercd0-E8vywpipKPA2lhBjQHAfQphEaZoHAEAGKmVDptITJwlhQwphGMpMCw7CHkWkZWTeQwLsAyLJGkmQ5LhN4MFgGDIvpZloEsQUxgFe5QXcyB1mF6ZLHFpCZsScAANqaFoGjaHlWgALoxeWd40AKGAgGgoWROFSxlTAFVVSVegEl8N7ACZfQwFsYBoMZcARmsUD8JmnTjeYlJMAY3i-mYln0eW6AwHgUB0r4JRwGwFzQH0ZjeOclzwFFGDzUm5a6PCi1Bk0cDeFpMpDVIo2SXuPyhhFEZ9PdEBtRd8K6PQhrmm1l1fPMVCMrsWARH0fTJFATKdH6bk3SGYZfQjf1wGAxjICB9VaLmfT6qDbVOEAA

[jxom]

Created a tracking issue: #381

[fubhy]

@mhmulford0 Type issue with the second ("dynamic") call aside, why are you doing that second decodeEventLog in the first place for this case? .getLogs() already does the decoding internally and returns changes[].args typed correctly.

[fubhy]

This would work just fine:

import { createPublicClient, http, parseAbiItem } from 'viem'
import { mainnet } from 'viem/chains'

const transport = http(
  'https://eth-mainnet.g.alchemy.com/v2/my-correct-api-key',
)

const client = createPublicClient({
  chain: mainnet,
  transport,
})

const BLOCK_INTERVAL = 250
let startBlock = 15390081

setInterval(async () => {
  console.log({ startBlock })
  const event = parseAbiItem(
    'event Transfer(address indexed from, address indexed to, uint256 value)',
  )
  const changes = await client.getLogs({
    address: '0xb24cd494faE4C180A89975F1328Eab2a7D5d8f11',
    event: event,
    fromBlock: BigInt(startBlock),
    toBlock: BigInt(startBlock + BLOCK_INTERVAL),
  })

  startBlock += BLOCK_INTERVAL

  for (const change of changes) {
    console.log(change.args)
  }
}, 1500)

[mulfdev]

@mhmulford0 Type issue with the second ("dynamic") call aside, why are you doing that second decodeEventLog in the first place for this case? .getLogs() already does the decoding internally and returns changes[].args typed correctly.

It appears I made an incorrect assumption when reading the docs! I presumed that getLogs retrieved them and decodeEventLog made them usable. The above code makes a lot more sense, thank you.