writeContract #

Executes a write function on a contract.

A "write" function on a Solidity contract modifies the state of the blockchain. These types of functions require gas to be executed, and hence a Transaction is needed to be broadcast in order to change the state.

Internally, writeContract uses a Wallet Client to call the sendTransaction action with ABI-encoded data.

Usage #

Below is a very basic example of how to execute a write function on a contract (with no arguments).

While you can use writeContract by itself, it is highly recommended to pair it with simulateContract to validate that the contract write will execute without errors.

import { publicClient, walletClient } from './client'
import { wagmiAbi } from './abi'

const { request } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
})
await walletClient.writeContract(request)

export const wagmiAbi = [
  ...
  {
    inputs: [],
    name: "mint",
    outputs: [],
    stateMutability: "nonpayable",
    type: "function",
  },
  ...
] as const;

import { createWalletClient, custom } from 'viem'
import { mainnet } from 'viem/chains'

export const walletClient = createWalletClient({
  chain: mainnet,
  transport: custom(window.ethereum)
})

Passing Arguments #

If your function requires argument(s), you can pass them through with the args attribute.

TypeScript types for args will be inferred from the function name & ABI, to guard you from inserting the wrong values.

For example, the mint function name below requires a tokenId argument, and it is typed as [number].

import { walletClient } from './client'
import { wagmiAbi } from './abi'

const { request } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420]
})
await walletClient.writeContract(request)

export const wagmiAbi = [
  ...
  {
    inputs: [{ name: "tokenId", type: "uint32" }],
    name: "mint",
    outputs: [],
    stateMutability: "nonpayable",
    type: "function",
  },
  ...
] as const;

import { createWalletClient, custom } from 'viem'
import { mainnet } from 'viem/chains'

export const walletClient = createWalletClient({
  chain: mainnet,
  transport: custom(window.ethereum)
})

Standalone #

If you don't need to perform validation on the contract write, you can also use it by itself:

import { walletClient } from './client'
import { wagmiAbi } from './abi'

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
})

export const wagmiAbi = [
  ...
  {
    inputs: [],
    name: "mint",
    outputs: [],
    stateMutability: "nonpayable",
    type: "function",
  },
  ...
] as const;

import { createWalletClient, custom } from 'viem'
import { mainnet } from 'viem/chains'

export const walletClient = createWalletClient({
  chain: mainnet,
  transport: custom(window.ethereum)
})

Return Value #

Hash

A Transaction Hash.

Unlike readContract, writeContract only returns a Transaction Hash. If you would like to retrieve the return data of a write function, you can use the simulateContract action – this action does not execute a transaction, and does not require gas (it is very similar to readContract).

Parameters #

address #

• Type: Address

The contract address.

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2', 
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420]
})

abi #

• Type: Abi

The contract's ABI.

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi, 
  functionName: 'mint',
  args: [69420]
})

functionName #

• Type: string

A function to extract from the ABI.

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint', 
  args: [69420]
})

account #

• Type: Address

The Account sender. Read more.

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  account: getAccount('0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266') 
})

accessList (optional) #

• Type: AccessList

The access list.

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  accessList: [{ 
    address: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
    storageKeys: ['0x1'],
  }], 
})

args (optional) #

• Type: Inferred from ABI.

Arguments to pass to function call.

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420] 
})

assertChain (optional) #

• Type: boolean
• Default: true

Throws an error if chain does not match the current wallet chain.

Defaults to true, but you can turn this off if your dapp is primarily multi-chain.

import { optimism } from 'viem/chains' 

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  assertChain: false, 
  chain: optimism, 
})

chain (optional) #

• Type: Chain
• Default: walletClient.chain

The target chain. If there is a mismatch between the wallet's current chain & the target chain, an error will be thrown if assertChain is truthy.

The chain is also used to infer its request type (e.g. the Celo chain has a gatewayFee that you can pass through to sendTransaction).

import { optimism } from 'viem/chains' 

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  chain: optimism, 
})

gasPrice (optional) #

• Type: bigint

The price (in wei) to pay per gas. Only applies to Legacy Transactions.

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  gasPrice: parseGwei('20'), 
})

maxFeePerGas (optional) #

• Type: bigint

Total fee per gas (in wei), inclusive of maxPriorityFeePerGas. Only applies to EIP-1559 Transactions

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  maxFeePerGas: parseGwei('20'),  
})

maxPriorityFeePerGas (optional) #

• Type: bigint

Max priority fee per gas (in wei). Only applies to EIP-1559 Transactions

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  maxFeePerGas: parseGwei('20'),
  maxPriorityFeePerGas: parseGwei('2'), 
})

nonce (optional) #

• Type: number

Unique number identifying this transaction.

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  nonce: 69 
})

value (optional) #

• Type: number

Value in wei sent with this transaction.

await walletClient.writeContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  value: parseEther('1') 
})

Live Example #

Check out the usage of writeContract in the live Writing to Contracts Example below.