> For the complete documentation index, see [llms.txt](/llms.txt).

# Call a contract

This tutorial uses Web3.js to execute a function in a smart contract. Calling the contract function is a type of transaction that requires paying gas.

## Prerequisites[​](#prerequisites "Direct link to Prerequisites")

Before attempting this tutorial, ensure you completed the tutorial to [deploy a contract](/services/tutorials/ethereum/deploy-a-contract-using-web3.js/) and [updated the .env file with the smart contract address](/services/tutorials/ethereum/deploy-a-contract-using-web3.js/#10-update-the-env-file).

## Steps[​](#steps "Direct link to Steps")

### 1\. Create a script to execute the contract[​](#1-create-a-script-to-execute-the-contract "Direct link to 1. Create a script to execute the contract")

In the `deployContract` folder created [earlier](/services/tutorials/ethereum/deploy-a-contract-using-web3.js/#2-create-a-project-directory), create the JavaScript file that executes a contract function and signs the transaction.

In this example we'll create the `call.js` file with the following contents:

```
const { Web3 } = require('web3')

// Loading the contract ABI
// (the results of a previous compilation step)
const fs = require('fs')
const { abi } = JSON.parse(fs.readFileSync('Demo.json'))

async function main() {
  // Configuring the connection to an Ethereum node
  const network = process.env.ETHEREUM_NETWORK
  const web3 = new Web3(
    new Web3.providers.HttpProvider(`https://${network}.infura.io/v3/${process.env.INFURA_API_KEY}`)
  )
  // Creating a signing account from a private key
  const signer = web3.eth.accounts.privateKeyToAccount('0x' + process.env.SIGNER_PRIVATE_KEY)
  web3.eth.accounts.wallet.add(signer)
  // Creating a Contract instance
  const contract = new web3.eth.Contract(
    abi,
    // Replace this with the address of your deployed contract
    process.env.DEMO_CONTRACT
  )
  // Issuing a transaction that calls the `echo` method
  const method_abi = contract.methods.echo('Hello, world!').encodeABI()
  const tx = {
    from: signer.address,
    to: contract.options.address,
    data: method_abi,
    value: '0',
    gasPrice: '100000000000',
  }
  const gas_estimate = await web3.eth.estimateGas(tx)
  tx.gas = gas_estimate
  const signedTx = await web3.eth.accounts.signTransaction(tx, signer.privateKey)
  console.log('Raw transaction data: ' + signedTx.rawTransaction)
  // Sending the transaction to the network
  const receipt = await web3.eth
    .sendSignedTransaction(signedTx.rawTransaction)
    .once('transactionHash', txhash => {
      console.log(`Mining transaction ...`)
      console.log(`https://${network}.etherscan.io/tx/${txhash}`)
    })
  // The transaction is now on chain!
  console.log(`Mined in block ${receipt.blockNumber}`)
}

require('dotenv').config()
main()

```

### 2\. Call the contract[​](#2-call-the-contract "Direct link to 2. Call the contract")

Run the script to call the smart contract:

```
node call.js

```

info

If you receive an `insufficient funds for gas` error, then you may need to top up your signer account with some testnet ETH.

The script will display the details of the transaction in the output. View the transaction in a block explorer such as Etherscan.