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中文 / English

Abstract

Through this basic task, you can learn the processes of compiling and deploying a smart contract, as well as learn how to use the basic APIs of web3js.

Preparation

  • You need to create a project on Infura, and get the PROJECT ID, change your ENDPOINTS to Sepolia;

  • Create an account on MetaMask, which is a browser extension;

    1. Get a wallet address, and the private key;
    2. Go Settings - advanced and open Show test networks;
      • Select Sepolia, and record this address
    3. Top up your account through faucets or others web services;
    4. Wait for minutes, and see the balance on MetaMask

  • Create a .env file, and add the following lines:

    PRIVATE_KEY=YOUR_PRIVATE_KEY
INFURA_ID=YOUR_PROJECT_ID

    | Note: You can check the .env.example file.

  • If you know Chinese, you can check these tasks on BILIBILI.

Getting Started

Understanding The Functions of the Smart Contract

  • Constructor: The constructor function of the smart contract, which is called when the contract is deployed, at the same time it will initialize the number to _initialNumber;
  • increment: The function of incrementing the number by given _value;
  • rest: The function of resetting the number to 0;
  • getNumber: The function of getting the number.

How to run it

  1. Please use node v20.11.0 to run following commands
  2. Install dependencies: npm install
  3. Copy the configuration file: cp .env.example .env
  4. Edit the configuration file: vim .env, copy your project ID and private key to the .env file 
    PRIVATE_KEY=YOUR_PRIVATE_KEY
INFURA_ID=YOUR_PROJECT_ID
  5. Run the index.js file: node index.js

Interpret the Code in index.js

index.js contains the most important part of this task, which includes the following functions:

1. Load the configuration file

For security sake, the private key is not hard-coded, but it can be read as environment variables. When run this task, the dotenv plugin will automatically read the configurations in the .env file and load them as environment variables, and then you can use the private key and other environment variables via process.env .
Here is the code:

require('dotenv').config();
const privatekey = process.env.PRIVATE_KEY;

2. Compile the smart contract file

You can not use .sol files directly, you need to compile it to binary file firstly.

Load the smart contract file Incrementer.sol into source variable.

// Load contract
const source = fs.readFileSync('Incrementer.sol', 'utf8');

Compile the smart contract file

const input = {
  language: 'Solidity',
  sources: {
    'Incrementer.sol': {
      content: source,
    },
  },
  settings: {
    outputSelection: {
      '*': {
        '*': ['*'],
      },
    },
  },
};

const tempFile = JSON.parse(solc.compile(JSON.stringify(input)));

| Note: The version of solidity in this task is 0.8.0, different versions may have different compile ways.

3. Get the bytecode and abi

const contractFile = tempFile.contracts['Incrementer.sol']['Incrementer'];

// Get bin & abi
const bytecode = contractFile.evm.bytecode.object;
const abi = contractFile.abi;

4. Create the web3 instance

web3 is the main API of the web3js library. It is used to interact with the blockchain.

// Create web3 with sepolia provider，you can change sepolia to other testnet
const web3 = new Web3('https://sepolia.infura.io/v3/' + process.env.INFURA_ID);

| Note: The INFURA_ID is the PROJECT ID of the Infura project you created in Preparation part.

5. Get the account address

On blockchain, each user has a address, which is unique for others, and you can get the address by the private key. In this task, you can use to web3.eth.accounts.privateKeyToAccount API to get your account address by passing the private key as a parameter.

// Create account from privatekey
const accounts = web3.eth.accounts.wallet.add(privatekey);

6. Get contract instance

In the 3rd step, you got the bytecode and abi, so you can create the contract instance by the abi

// Create contract instance
const deployContract = new web3.eth.Contract(abi);

7. Create the deploy transaction

// Create Tx
const deployTx = deployContract.deploy({
  data: '0x' + bytecode,
  arguments: [0], // Pass arguments to the contract constructor on deployment(_initialNumber in Incremental.sol)
});

8. Deploy your smart contract

Use your private key to sign the deploy transaction.

const tx = await deployTx.send({
  from: accounts[0].address,
  gas,
  // gasPrice: 10000000000,
});

References