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simulateContract

The simulateContract function simulates/validates a contract interaction. This is useful for retrieving return data and revert reasons of contract write functions.

This function does not require gas to execute and does not change the state of the blockchain. It is almost identical to readContract, but also supports contract write functions.

Internally, simulateContract uses a Public Client to call the call action with ABI-encoded data.

Usage

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

The mint function accepts no arguments, and returns a token ID.

ts
import { publicClient } from './client'
import { wagmiAbi } from './abi'

const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
})
// 69420
ts
export const wagmiAbi = [
  ...
  {
    inputs: [],
    name: "mint",
    outputs: [{ name: "", type: "uint32" }],
    stateMutability: "view",
    type: "function",
  },
  ...
] as const;
ts
import { createPublicClient, http } from 'viem'
import { mainnet } from 'viem/chains'

export const publicClient = createPublicClient({
  chain: mainnet,
  transport: http()
})

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

const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
})
// 69420
ts
export const wagmiAbi = [
  ...
  {
    inputs: [{ name: "owner", type: "uint32" }],
    name: "mint",
    outputs: [{ name: "", type: "uint32" }],
    stateMutability: "view",
    type: "function",
  },
  ...
] as const;
ts
import { createPublicClient, http } from 'viem'
import { mainnet } from 'viem/chains'

export const publicClient = createPublicClient({
  chain: mainnet,
  transport: http()
})

Pairing with writeContract

The simulateContract function also pairs well with writeContract.

In the example below, we are validating if the contract write will be successful via simulateContract. If no errors are thrown, then we are all good. After that, we perform a contract write to execute the transaction.

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

const { request } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
})
const hash = await walletClient.writeContract(request)
ts
export const wagmiAbi = [
  ...
  {
    inputs: [],
    name: "mint",
    outputs: [{ name: "", type: "uint32" }],
    stateMutability: "view",
    type: "function",
  },
  ...
] as const;
ts
import { createPublicClient, http } from 'viem'
import { mainnet } from 'viem/chains'

export const publicClient = createPublicClient({
  chain: mainnet,
  transport: http()
})

Return Value

The response from the contract. Type is inferred.

Parameters

address

  • Type: Address

The contract address.

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2', 
  abi: wagmiAbi,
  functionName: 'mint',
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
})

abi

The contract's ABI.

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi, 
  functionName: 'mint',
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
})

functionName

  • Type: string

A function to extract from the ABI.

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint', 
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
})

from

  • Type: Address

The sender of the call.

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266' 
})

accessList (optional)

The access list.

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  accessList: [{ 
    address: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
    storageKeys: ['0x1'],
  }], 
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
})

args (optional)

  • Type: Inferred from ABI.

Arguments to pass to function call.

ts
const { result } = await publicClient.simulateContract({
  address: '0x1dfe7ca09e99d10835bf73044a23b73fc20623df',
  abi: wagmiAbi,
  functionName: 'balanceOf',
  args: ['0xa5cc3c03994DB5b0d9A5eEdD10CabaB0813678AC'], 
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
})

gasPrice (optional)

  • Type: bigint

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

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
  gasPrice: parseGwei('20'), 
})

maxFeePerGas (optional)

  • Type: bigint

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

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
  maxFeePerGas: parseGwei('20'),  
})

maxPriorityFeePerGas (optional)

  • Type: bigint

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

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
  maxFeePerGas: parseGwei('20'),
  maxPriorityFeePerGas: parseGwei('2'), 
})

nonce (optional)

  • Type: number

Unique number identifying this transaction.

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
  nonce: 69 
})

value (optional)

  • Type: number

Value in wei sent with this transaction.

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  args: [69420],
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
  value: parseEther('1') 
})

blockNumber (optional)

  • Type: number

The block number to perform the read against.

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
  blockNumber: 15121123n, 
})

blockTag (optional)

  • Type: 'latest' | 'earliest' | 'pending' | 'safe' | 'finalized'
  • Default: 'latest'

The block tag to perform the read against.

ts
const { result } = await publicClient.simulateContract({
  address: '0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2',
  abi: wagmiAbi,
  functionName: 'mint',
  from: '0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266',
  blockTag: 'safe', 
})

Released under the MIT License.

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