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Web3js ERC20

This basic task is to show how to interact with ERC20 contract, so the developer can understand the basic interface of ERC20 contract.

Getting started

SimpleToken contract function description

  • IERC20 totalSupply: Get the total amount of ERC20 token in the contract balanceOf: Get the amount of ERC20 token of specific account in the contract transfer: Transfer ERC20 token to specific account allowance: Get the amount of ERC20 tokens of the source account that the target account can use approve: Authorize the target account to transfer the specified amount of ERC20 Tokens transferFrom: (Third party call) Transfer a specific amount of ERC20 token from the source account to target account

  • IERC20Metadata name: Get the name of the Token symbol: Get the symbol of the Token decimals: Get the decimals of the Token

How to run it

  1. Install dependencies: npm install
  2. Copy the configuration file: cp .env.example .env
  3. 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
  4. Run the index.js file: node index.js

Interpret Source Code

compile.js

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

  1. Load the smart contract file SimpleToken.sol into source variable.
// Load contract
const source = fs.readFileSync('SimpleToken.sol', 'utf8');
  1. Compile the smart contract file
// compile solidity
const input = {
    language: 'Solidity',
    sources: {
    'SimpleToken.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.

  1. Get the Contract Binary Object

The solidity object that was successfully compiled in the previous step contains many properties/values, and what we only need is the contract object, so we can get the SimpleToken contract object by accessing the object properties.

const contractFile = tempFile.contracts['SimpleToken.sol']['SimpleToken'];
  1. Export contractFile Object If you want to use the contractFile object in other js files, you can export it.
module.exports = contractFile;

index.js

  1. Load the SimpleToken smart contract from compile file
const contractFile = require('./compile');
  1. Load private key

For security’s 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.

require('dotenv').config();
const privatekey = process.env.PRIVATE_KEY;
  1. Create a receiver account for testing
const receiver = '0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266';
  1. Build the web3 object
const web3 = new Web3(new Web3.providers.HttpProvider('https://goerli.infura.io/v3/' + process.env.INFURA_ID));

| Note: The INFURA_ID is the PROJECT ID of the Infura project you created in last task

  1. 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 the we3.eth.accounts.privateKeyToAccount API to get your account address by passing the private key as a parameter.

const account = web3.eth.accounts.privateKeyToAccount(privatekey);
const account_from = {
    privateKey: account.privateKey,
    accountaddress: account.address,
};
  1. Get the abi and bin When deploying the smart contract, we need two important parameters which are the bytecode and abi of the smart contract. In previous step 1, we loaded the compiled SimpleToken object, so we can get the bytecode and abi from it.
const bytecode = contractFile.evm.bytecode.object;
const abi = contractFile.abi;
  1. Get contract instance In the last step, you got the bin and abi, so we can create the contract instance by the abi.
const deployContract = new web3.eth.Contract(abi);
  1. Create the transaction of the deployContract
const deployTx = deployContract.deploy({
    data: bytecode,
    arguments: ['DAPPLEARNING', 'DAPP', 0, 10000000],
});

| So far, this transaction has not been deployed into the blockchain.

  1. Sign the transaction Use your private key to sign the transaction.
const deployTransaction = await web3.eth.accounts.signTransaction(
    {
    data: deployTx.encodeABI(),
    gas: '8000000',
    },
    account_from.privateKey
);
  1. Deploy the contract Send your signed deployTransaction transaction to the blockchain. You will receive a receipt, and get this contract address from it.
const deployReceipt = await web3.eth.sendSignedTransaction(deployTransaction.rawTransaction);
console.log(`Contract deployed at address: ${deployReceipt.contractAddress}`);
  1. Create a transfer transaction

We created a transfer transaction for ERC20 token, the receiver is receiver account, and the amount is 100000 token.

const transferTx = erc20Contract.methods.transfer(receiver, 100000).encodeABI();
  1. Sign and send the transaction
const transferReceipt = await web3.eth.sendSignedTransaction(transferTransaction.rawTransaction);
  1. Check the balance of the receiver account

After the transaction is sent, you can log the balance of the receiver and make sure the balance is correct.

erc20Contract.methods
    .balanceOf(receiver)
    .call()
    .then((result) => {
    console.log(`The balance of receiver is ${result}`);
    });

Notes

  • infura doesn't support sendTransaction, only support sendRawTransaction
  • infura doesn't invoke eth_sendTransaction, so you need to an unlocked account on the ethereum node. More details, please refer to this

References