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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.

WARNING

The writeContract internally sends a transaction – it does not validate if the contract write will succeed (the contract may throw an error). It is highly recommended to simulate the contract write with simulateContract before you execute it.

Import

ts
import { writeContract } from 'viem/contract'

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.

ts
import { writeContract } from 'viem/contract'
import { publicClient, walletClient } from './client'
import { wagmiAbi } from './abi'

const { request } = await simulateContract(publicClient, {
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
})
await writeContract(walletClient, request)
ts
export const wagmiAbi = [
  ...
  {
    inputs: [],
    name: "mint",
    outputs: [],
    stateMutability: "nonpayable",
    type: "function",
  },
  ...
] as const;
ts
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].

ts
import { writeContract } from 'viem/contract'
import { walletClient } from './client'
import { wagmiAbi } from './abi'

const { request } = await simulateContract(publicClient, {
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420]
})
await writeContract(walletClient, request)
ts
export const wagmiAbi = [
  ...
  {
    inputs: [{ name: "tokenId", type: "uint32" }],
    name: "mint",
    outputs: [],
    stateMutability: "nonpayable",
    type: "function",
  },
  ...
] as const;
ts
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:

ts
import { writeContract } from 'viem/contract'
import { walletClient } from './client'
import { wagmiAbi } from './abi'

await writeContract(walletClient, {
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
})
ts
export const wagmiAbi = [
  ...
  {
    inputs: [],
    name: "mint",
    outputs: [],
    stateMutability: "nonpayable",
    type: "function",
  },
  ...
] as const;
ts
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.

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

abi

The contract's ABI.

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

functionName

  • Type: string

A function to extract from the ABI.

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

accessList (optional)

The access list.

ts
await writeContract(walletClient, {
  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.

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

from (optional)

  • Type: Address

Optional sender override.

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

gasPrice (optional)

  • Type: bigint

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

ts
await writeContract(walletClient, {
  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

ts
await writeContract(walletClient, {
  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

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

nonce (optional)

  • Type: number

Unique number identifying this transaction.

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

value (optional)

  • Type: number

Value in wei sent with this transaction.

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

Released under the MIT License.

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