Chain Properties

Some chains support additional properties related to blocks and transactions. This is powered by Viem's formatters and serializers. For example, Celo, ZkSync, OP Stack chains support all support additional properties. In order to use these properties in a type-safe way, there are a few things you should be aware of.

Narrowing Parameters

When you pass your config to an action, you are ready to access chain-specific properties! For example, Celo's feeCurrency is available.

index.ts

import { parseEther } from 'viem'
import { simulateContract } from '@wagmi/core'
import { config } from './config'

const result = await simulateContract(config, {
  to: '0xd2135CfB216b74109775236E36d4b433F1DF507B',
  value: parseEther('0.01'),
  feeCurrency: '0x…', 
})

config.ts

import { http, createConfig } from '@wagmi/core'
import { base, celo, mainnet } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [base, celo, mainnet],
  transports: {
    [base.id]: http(),
    [celo.id]: http(),
    [mainnet.id]: http(),
  },
})

This is great, but if you have multiple chains that support additional properties, your autocomplete could be overwhelmed with all of them. By setting the chainId property to a specific value (e.g. celo.id), you can narrow parameters to a single chain.

index.ts

import { parseEther } from 'viem'
import { simulateContract } from '@wagmi/core'
import { celo } from 'wagmi/chains'

const result = await simulateContract({
  to: '0xd2135CfB216b74109775236E36d4b433F1DF507B',
  value: parseEther('0.01'),
  chainId: celo.id, 
  feeCurrency: '0x…', 
  // ^? (property) feeCurrency?: `0x${string}` | undefined
})

config.ts

import { http, createConfig } from '@wagmi/core'
import { base, celo, mainnet } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [base, celo, mainnet],
  transports: {
    [base.id]: http(),
    [celo.id]: http(),
    [mainnet.id]: http(),
  },
})

Narrowing Return Types

Return types can also have chain-specific properties attached to them. There are a couple approaches for extracting these properties.

chainId Parameter

Not only can you use the chainId parameter to narrow parameters, you can also use it to narrow the return type.

index.tsx

import { waitForTransactionReceipt } from '@wagmi/core'
import { zkSync } from '@wagmi/core/chains'

const result = await waitForTransactionReceipt({
  chainId: zkSync.id,
  hash: '0x16854fcdd0219cacf5aec5e4eb2154dac9e406578a1510a6fc48bd0b67e69ea9',
})

result.logs
//     ^? (property) logs: ZkSyncLog[] | undefined

config.ts

import { http, createConfig } from '@wagmi/core'
import { base, celo, mainnet } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [base, celo, mainnet],
  transports: {
    [base.id]: http(),
    [celo.id]: http(),
    [mainnet.id]: http(),
  },
})

chainId Data Property

Wagmi internally will set a chainId property on return types that you can use to narrow results. The chainId is determined from the chainId parameter or global state (e.g. connector). You can use this property to help TypeScript narrow the type.

index.tsx

import { waitForTransactionReceipt } from '@wagmi/core'
import { zkSync } from '@wagmi/core/chains'

const result = await waitForTransactionReceipt({
  hash: '0x16854fcdd0219cacf5aec5e4eb2154dac9e406578a1510a6fc48bd0b67e69ea9',
})

if (result.chainId === zkSync.id) {
  result.logs
  //     ^? (property) logs: ZkSyncLog[] | undefined
}

config.ts

import { http, createConfig } from '@wagmi/core'
import { base, celo, mainnet } from '@wagmi/core/chains'

export const config = createConfig({
  chains: [base, celo, mainnet],
  transports: {
    [base.id]: http(),
    [celo.id]: http(),
    [mainnet.id]: http(),
  },
})

Troubleshooting

If chain properties aren't working, make sure TypeScript is configured correctly. Not all chains have additional properties, to check which ones do, see the Viem repo (chains that have a top-level directory under src/chains support additional properties).