Events and Function chaining

This page shows how to link your Mimic functions by emitting and listening to custom events. You’ll learn the full flow:

1. Emitting an event from a function

2. Creating an event trigger to trigger another function from the event

3. Reading the event data in the triggered function

Pre-reqs: You’ve already read the basic function guide and can mimic codegen, mimic compile, and mimic deploy.

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Emit a custom event

Goal: Add an event with arbitrary information to an operation so it's emitted on-chain when the intent is executed.

Events are attached to operations (not to the intent itself), so you call .addEvent() on any operation builder — EvmCallBuilder, SwapBuilder, or TransferBuilder — before calling .send().

import { Address, Bytes, ChainId, Ethereum, EvmCallBuilder, evm, EvmEncodeParam, TokenAmount } from '@mimicprotocol/lib-ts'

export default function main(): void {
  const topic = evm.keccak('First function')
  const data = evm.encode([EvmEncodeParam.fromValue('address', '0xSomeAddress')])
  const fee = TokenAmount.fromStringDecimal(Ethereum.USDC, '1')

  EvmCallBuilder.forChain(ChainId.ETHEREUM)
    .addCall(Address.fromString('0xContractAddress'), callData)
    .addEvent(Bytes.fromHexString(topic), Bytes.fromHexString(data))
    .addUser('0xSmartAccountAddress')
    .send(fee)
}

The same .addEvent() method is available on SwapBuilder and TransferBuilder:

SwapBuilder.forChains(ChainId.ETHEREUM, ChainId.OPTIMISM)
  .addTokenInFromStringDecimal(Ethereum.USDC, '1000')
  .addTokenOutFromStringDecimal(Optimism.USDC, '990', recipient)
  .addEvent(Bytes.fromHexString(topic), Bytes.fromHexString(data))
  .send()

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Trigger a function from a custom event

Goal: Automatically execute a second function every time an intent from the first function is executed.

import { Chains, Client, TriggerType } from '@mimicprotocol/sdk'
import { AbiCoder, keccak256, toUtf8Bytes } from 'ethers'

async function main(): Promise<void> {
  const MIMIC_PROTOCOL_SETTLER = '0xSettlerAddress'
  const INTENT_EXECUTED_TOPIC = '0xee2c98c99b683f71058b8744fea294a411482f07d55c98b392917e9286f22f13'
  const USER_TOPIC = AbiCoder.defaultAbiCoder().encode(['address'], ['0xUserAddress'])
  const FIRST_FUNCTION_TOPIC = keccak256(toUtf8Bytes('First function'))

  const config = {
    type: TriggerType.Event
    chainId: Chains.SomeChain,
    contract: MIMIC_PROTOCOL_SETTLER,
    topics: [
      [INTENT_EXECUTED_TOPIC],
      [USER_TOPIC],
      [FIRST_FUNCTION_TOPIC],
    ],
  }

  const client = new Client({ signer })
  await client.triggers.signAndCreate({ SECOND_FUNCTION_CID, config, ... })
}

Notes

• The code above is a backend script, not a function.

• This section shows how to trigger a function from a custom event. However, it's also possible to trigger functions from any smart contract event, such as ERC-20 token transfers.

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Read event data

Goal: Access information included in the event.

import { Address, environment, evm } from '@mimicprotocol/lib-ts'
import { IntentExecutedEvent } from './types/Settler'

export default function main(): void {
  const trigger = environment.getContext().triggerPayload.getEventData()
  const event = IntentExecutedEvent.decode(trigger.topics, trigger.eventData)
  const str = evm.decode(new EvmDecodeParam('address', event.data.toHexString()))
  const someAddress = Address.fromString(str) // 0xSomeAddress
}

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Use case

For a complete use case using custom events, see Bridge and invest in Aave, where one function transfers tokens between chains and emits an event, and another function reacts to that event by investing the bridged tokens.