How to Integrate Smart Contracts with Express.js for Blockchain Apps

Smart contracts are self-executing contracts with the terms of the agreement written directly into lines of code. They have the potential to revolutionize the way we do business, making transactions more secure, transparent, and efficient.

Express.js is a popular Node.js framework for building web applications. It provides a flexible and modular way to build web applications, making it an ideal choice for building blockchain-based applications.

Prerequisites

Before we begin, make sure you have the following installed:

• Node.js
• Express.js
• Web3.js
• Truffle Suite

Step 1: Set up the Project

Create a new directory for your project and navigate to it in your terminal. Then, run the following command to create a new Node.js project:

npm init

Next, install the required dependencies:

npm install express web3 truffle-suite

Step 2: Create the Smart Contract

Create a new file called `MyContract.sol` and add the following code:

pragma solidity ^0.8.0;

contract MyContract {
    address private owner;

    constructor() public {
        owner = msg.sender;
    }

    function getOwner() public view returns (address) {
        return owner;
    }
}

This is a simple smart contract that has a single function `getOwner()` that returns the address of the contract owner.

Step 3: Deploy the Smart Contract

Deploy the smart contract to the Ethereum blockchain using Truffle Suite:

truffle migrate --network ropsten

This will deploy the smart contract to the Ropsten test network.

Step 4: Create the Express.js App

Create a new file called `app.js` and add the following code:

const express = require('express');
const Web3 = require('web3');
const MyContract = require('./MyContract.json');

const app = express();

const web3 = new Web3(new Web3.providers.HttpProvider('https://ropsten.infura.io/v3/YOUR_PROJECT_ID'));

const contract = new web3.eth.Contract(MyContract.abi, MyContract.address);

app.get('/getOwner', async (req, res) => {
  const owner = await contract.methods.getOwner().call();
  res.send({ owner });
});

app.listen(3000, () => {
  console.log('Server listening on port 3000');
});

This code creates an Express.js app that listens for GET requests to the `/getOwner` endpoint. When a request is received, it calls the `getOwner()` function on the smart contract and returns the result as a JSON response.

Conclusion

In this tutorial, we learned how to integrate smart contracts with Express.js for blockchain apps. We created a simple smart contract, deployed it to the Ethereum blockchain, and created an Express.js app that interacts with the smart contract.

Watch the video tutorial below for a more detailed explanation:

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