Welcome to the World of Blockchain Development


Welcome to this comprehensive course designed to set you on the path to becoming a blockchain developer. The fascinating world of blockchain technology has experienced significant growth over the past decade and continues to evolve. The demand for professionals skilled in blockchain development is skyrocketing, with opportunities in various industries beyond just finance.

This course aims to take you from the basics of blockchain technology to creating your own decentralized applications (dApps) using Solidity and JavaScript. Whether you are a newcomer to programming or an experienced developer looking to expand your skill set, this course has something to offer.

Exploring the Core Concepts of Blockchain Technology

To lay a solid foundation for understanding blockchain technology, we will explore its core concepts and transformative potential. This understanding will help you grasp how digital currencies like Ethereum work, what smart contracts are, and why they are revolutionary.

Mastering Solidity for Smart Contracts

In this course, we will dive into Solidity, the primary programming language used for writing smart contracts on the Ethereum blockchain. You will learn the syntax, data types, and control structures of Solidity, along with best practices for security and efficiency.

Full-Stack Web3 Development

As we progress, we will explore full-stack Web3 development. You will learn how to create user-friendly interfaces for your dApps using JavaScript, one of the most popular programming languages in the web development world.

By the end of this course, you will have hands-on experience developing dApps and a deep understanding of the tools, techniques, and software that blockchain developers use daily. This includes Remix, Ethers.js, Hardhat, and more.

Welcome To Blockchain

Welcome to the world of Blockchain! Blockchain technology enables the creation of a decentralized digital ledger of transactions on a distributed network. This ledger is accessible to all network participants, promoting transparency and accountability. Blockchain serves as the foundation for cryptocurrencies, smart contracts, and much more.

Blockchain Basics

Blockchain consists of a series of blocks, with each block holding a list of transactions. Once a block is added to the chain, the information within it becomes viewable to everyone on the network and remains immutable. The blockchain is maintained by nodes or computers, each having a copy of the entire blockchain.

Welcome to Remix! Simple Storage

Remix is a powerful, open-source tool that allows you to write Solidity contracts directly from your browser. Solidity is a programming language used to implement smart contracts, particularly on Ethereum. Let’s begin by creating a simple storage contract in Remix. This contract will enable you to store and retrieve a number. Here’s how it looks in Solidity:

pragma solidity ^0.8.0;

contract SimpleStorage {
    uint public data;

    function set(uint x) public {
        data = x;

    function get() public view returns (uint) {
        return data;

Remix Storage Factory

Let’s now introduce a bit more complexity by creating a contract that deploys our SimpleStorage contract. This new contract will act as our StorageFactory.

pragma solidity ^0.8.0;

import "./SimpleStorage.sol";

contract StorageFactory {
    SimpleStorage[] public simpleStorageArray;

    function createSimpleStorageContract() public {
        SimpleStorage simpleStorage = new SimpleStorage();
    //... more code here ...

Remix Fund Me

The ‘Fund Me’ contract is a simple crowdfunding contract where users can donate money to the contract owner. The owner can then withdraw funds when needed. Below is a basic example:

pragma solidity ^0.8.0;

contract FundMe {
    mapping(address => uint) public contributors;
    address public admin;

    constructor() {
        admin = msg.sender;

    function contribute() public payable {
        contributors[msg.sender] += msg.value;

    function getBalance() public view returns(uint) {
        return address(this).balance;

    function withdraw() public {
        require(msg.sender == admin, "Only admin can withdraw");

The next sections will show you how to interact with these contracts using Ethers.js and Hardhat, as well as how to create a frontend for these contracts using HTML/JavaScript and Next.js. We will also delve into more complex topics such as ERC20s, DeFi, Aave, NFTs, DAOs, and more.

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Remember, the key to mastering these concepts is practice. Try creating your own contracts, modifying existing ones, and always strive to understand what every line of code is doing. Don’t just copy-paste!

Ethers.js Simple Storage

Ethers.js is a JavaScript library that simplifies interaction with the Ethereum blockchain and smart contracts. Let’s use Ethers.js to interact with our SimpleStorage contract:

First, install ethers.js using npm:

npm install -save ethers

Then, you can interact with your SimpleStorage contract like this:

const ethers = require('ethers');

// Connect to the network
let provider = ethers.getDefaultProvider('ropsten');

// The address that the Contract WILL have once mined
let contractAddress = "your_contract_address_here";

// The ABI (interface)
let abi = [
    "function get() view returns (uint)",
    "function set(uint)"

// Init contract
let contract = new ethers.Contract(contractAddress, abi, provider);

// Call the contract's 'get' function
let value = await contract.get();
console.log('Stored value in Remix contract:', value.toString());

// Set a new value (only works if you're the contract owner)
let newValue = 7;
let tx = await contract.set(newValue);
await tx.wait();

Hardhat Simple Storage

Hardhat is a development environment for Ethereum software. It provides a seamless experience for compiling, deploying, testing, and debugging your Ethereum applications. Let’s use Hardhat to deploy and interact with our SimpleStorage contract.

First, install Hardhat using npm:

npm install -save-dev hardhat

Next, create a Hardhat config file (hardhat.config.js) and set up a local Ethereum network:

module.exports = {
    networks: {
        hardhat: {
            chainId: 1337
    solidity: "0.8.0",

You can then deploy and interact with your SimpleStorage contract in a script:

const ethers = require('ethers');
const { ethers } = hre;

async function main() {
    const SimpleStorage = await hre.ethers.getContractFactory("SimpleStorage");
    const simpleStorage = await SimpleStorage.deploy();
    await simpleStorage.deployed();
    console.log("SimpleStorage deployed to:", simpleStorage.address);

    let tx = await simpleStorage.set(23);
    await tx.wait();

    let value = await simpleStorage.get();
    console.log('Stored value in Hardhat contract:', value.toString());


Hardhat Fund Me

Similarly, you can deploy your FundMe contract using Hardhat:

const ethers = require('ethers');
const { ethers } = hre;

async function main() {
    const FundMe = await hre.ethers.getContractFactory("FundMe");
    const fundMe = await FundMe.deploy();
    await fundMe.deployed();
    console.log("FundMe deployed to:", fundMe.address);


You can then contribute to the contract and check its balance like this:

let tx = await fundMe.contribute({ value: ethers.utils.parseEther("1.0") });
await tx.wait();

let balance = await fundMe.getBalance();
console.log('Contract balance:', ethers.utils.formatEther(balance));

HTML / JavaScript Fund Me (Full Stack / Front End)

To interact with your smart contracts from a webpage, we can use JavaScript along with the ethers.js library. Let’s create a simple HTML page to interact with our FundMe contract:

<!DOCTYPE html>
    <button id="contribute">Contribute</button>
    <button id="getBalance">Get Balance</button>
    <div id="balance"></div>
<script src="https://cdn.ethers.io/lib/ethers-5.0.umd.min.js" type="application/javascript"></script>
<script src="app.js"></script>

In app.js, you can use ethers.js to interact with the contract:

const provider = new ethers.providers.Web3Provider(window.ethereum);
const signer = provider.getSigner();
const contractAddress = "your_contract_address_here";

const contractABI = [
    "function contribute() public payable",
    "function getBalance() public view returns (uint)",
    "function withdraw() public"

const fundMeContract = new ethers.Contract(contractAddress, contractABI, signer);

document.getElementById('contribute').addEventListener('click', async () => {
    const tx = await fundMeContract.contribute({ value: ethers.utils.parseEther("0.1") });
    await tx.wait();

document.getElementById('getBalance').addEventListener('click', async () => {
    const balance = await fundMeContract.getBalance();
    document.getElementById('balance').innerText = `Balance: ${ethers.utils.formatEther(balance)} ETH`;

Hardhat ERC20s

ERC20 is a widely adopted standard for tokens on the Ethereum blockchain. Let’s create an ERC20 token using Hardhat.

First, install the OpenZeppelin library, which provides secure and audited smart contracts:

npm install @openzeppelin/contracts

Now, create a new contract MyToken.sol and use the ERC20 implementation from OpenZeppelin:

// contracts/MyToken.sol
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract MyToken is ERC20 {
    constructor(uint256 initialSupply) ERC20("MyToken", "MTK") {
        _mint(msg.sender, initialSupply);

You can then write a script to deploy your token:

// scripts/deploy.js
async function main() {
    const [deployer] = await ethers.getSigners();
    console.log("Deploying contracts with the account:", deployer.address);

    const Token = await ethers.getContractFactory("MyToken");
    const token = await Token.deploy(1000000);

    console.log("Token address:", token.address);


Hardhat DeFi & Aave

Aave is a decentralized finance (DeFi) lending protocol that allows users to lend and borrow various cryptocurrencies with variable and stable interest rates. You can integrate Aave into your Hardhat project to interact with the Aave protocol. We will cover DeFi and Aave in more detail in later sections.

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Hardhat NFTs

Non-Fungible Tokens (NFTs) represent ownership of unique items or assets on the blockchain. They can be used to represent real-world or virtual assets. To create an NFT, we use the ERC721 standard. Using OpenZeppelin, creating an NFT is straightforward:

// contracts/MyNFT.sol
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

contract MyNFT is ERC721 {
    constructor() ERC721("MyNFT", "MNFT") {}

    function mint(address to, uint256 tokenId) public {
        _mint(to, tokenId);

Next.js NFT Marketplace (Full Stack / Front End)

After setting up our NFT contract, let’s build a frontend to interact with it. We’ll use Next.js and ethers.js to build an NFT marketplace where users can mint and view NFTs.

First, create a new file in the pages directory called nft.js:

import { ethers } from 'ethers';
import { useState } from 'react';

export default function NFTMarket() {
    const [tokenID, setTokenID] = useState(0);

    async function mintNFT() {
        const provider = new ethers.providers.Web3Provider(window.ethereum);
        const signer = provider.getSigner();
        const contractAddress = "your_NFT_contract_address_here";
        const contractABI = [
            "function mint(address to, uint256 tokenId) public"

        const nftContract = new ethers.Contract(contractAddress, contractABI, signer);
        const tx = await nftContract.mint(signer.getAddress(), tokenID);
        await tx.wait();

        setTokenID(tokenID + 1);

    return (
            <button onClick={mintNFT}>Mint NFT</button>
            <p>Minted NFTs: {tokenID}</p>

Hardhat Upgrades

When developing smart contracts, it’s crucial to consider upgradability. Hardhat provides the Hardhat Upgrades plugin, which allows you to create upgradable contracts.

To use Hardhat Upgrades, install it with the following command:

npm install @openzeppelin/hardhat-upgrades

Next, require it in your hardhat.config.js:


module.exports = {
    solidity: "0.8.4",

Now you can deploy your contracts as upgradable. An upgradable contract can be deployed using the deployProxy function and upgraded using the upgradeProxy function. Here’s an example:

const { ethers, upgrades } = require("hardhat");

async function main() {
    const MyContract = await ethers.getContractFactory("MyContract");
    const instance = await upgrades.deployProxy(MyContract);
    console.log("Deployed at:", instance.address);


Hardhat DAOs

Decentralized Autonomous Organizations (DAOs) are organizations governed by code and built on the blockchain. Implementing a DAO involves creating a smart contract that enables token holders to propose and vote on proposals. Here’s a simple implementation:

// contracts/SimpleDAO.sol
pragma solidity ^0.8.0;

contract SimpleDAO {
    struct Proposal {
        string description;
        uint voteCount;

    mapping(address => bool) public voters;
    Proposal[] public proposals;

    function propose(string memory description) public {
        voters[msg.sender] = true;
        proposals.push(Proposal({ description: description, voteCount: 0 }));

    function vote(uint proposalIndex) public {
        require(voters[msg.sender], "Only voters can vote");

Security and Auditing

Security is paramount when developing smart contracts. Conducting regular audits of your contracts is crucial for ensuring their security. Audits involve meticulously reviewing the contract code to identify potential vulnerabilities.

During an audit, you should:

  1. Check for common vulnerabilities such as re-entrancy, integer overflow, and underflow, and ensure your contracts use up-to-date versions of Solidity.
  2. Ensure your contracts have appropriate access controls and correct function visibility.
  3. Check that your contracts handle exceptions properly and have a safe fallback function.
  4. Ensure any external contract calls are handled correctly.
  5. Thoroughly test your contracts by writing unit tests and using coverage analysis. Consider using property-based and fuzz testing.
  6. Utilize static analysis tools like Slither or Securify.

Contract auditing is complex and requires a good understanding of Ethereum and Solidity. It is advisable to have your contracts audited by professionals, especially if they manage significant amounts of value.

Wrapping up, blockchain development is a vast and exciting field, with Ethereum leading the way in the decentralized world. Keep practicing, learning, and never stop building. As the blockchain space continues to grow, so will the opportunities it offers. This tutorial has provided you with the necessary tools and knowledge to start your journey as a blockchain developer.

What is Remix?

Remix is an open-source web and desktop application used for developing, testing, and debugging smart contracts written in the Solidity programming language for Ethereum. It provides an easy-to-use interface and a powerful Solidity editor with features like syntax highlighting and auto-completion.

What is Ethers.js?

Ethers.js is a complete and compact JavaScript library for interacting with the Ethereum blockchain. It allows you to create wallets, sign transactions, interact with smart contracts, and perform various other operations. Ethers.js is a lightweight alternative to web3.js and is preferred by many developers for its cleaner API and modular design.

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What is the difference between Web3.js and Ethers.js?

Both web3.js and ethers.js are libraries used to interact with the Ethereum blockchain. They provide similar functionalities such as sending transactions and interacting with smart contracts. However, there are some differences between them.

Web3.js was the first library of its kind and is more widely known. It offers comprehensive features but can be complex and inconsistent in its API design. On the other hand, ethers.js came later and provides a more compact, consistent, and modular API. It is often preferred by developers due to its cleaner syntax and improved usability.

What is Hardhat?

Hardhat is a development environment for Ethereum software. It simplifies the process of compiling, deploying, testing, and debugging Ethereum applications. Hardhat introduces new features and improvements to enhance JavaScript and Solidity development. It is known for its advanced debugging capabilities, flexible configuration, and support for TypeScript.

Is Solidity harder than Python?

Solidity and Python are different programming languages with their own complexities. Python is often recommended for beginners due to its simplicity and readability, making it easier to grasp, especially for those new to programming. On the other hand, Solidity is a statically typed language with a syntax closer to JavaScript and C++. Learning Solidity may be more challenging than learning Python, primarily because Solidity involves understanding blockchain concepts, and its environment has unique aspects such as gas fees and immutability.

However, with dedication and the right resources, Solidity is certainly learnable. There is a growing ecosystem of educational content and development tools to assist you. It is advisable to have a solid understanding of blockchain technology before diving into Solidity.

Is Solidity difficult to learn?

The difficulty of learning Solidity can vary depending on your prior programming and blockchain experience. If you are familiar with JavaScript or another C-style language and have a basic understanding of blockchain technology, you may find the syntax of Solidity familiar, making it easier to learn.

However, writing smart contracts in Solidity requires understanding specific principles related to the blockchain, such as how transactions work, gas fees, immutability, and more. Even experienced developers will need to learn and adapt to these new concepts.

Furthermore, Solidity’s environment is less forgiving than most programming environments. Mistakes can be costly because once a contract is deployed on the blockchain, it cannot be altered. Therefore, it is important to thoroughly understand the code you write and thoroughly test it.

Despite these challenges, with the right resources and dedication, Solidity is certainly learnable. There is a growing ecosystem of educational content and development tools to assist you. It is advisable to have a solid understanding of blockchain technology before diving into Solidity.

What is EVM?

The EVM, or Ethereum Virtual Machine, is the runtime environment for executing smart contracts in Ethereum. It is a decentralized, sandboxed virtual machine that ensures the execution of smart contracts is deterministic and secure.

Each Ethereum node runs its own EVM implementation and independently executes the same instructions for every smart contract. This consensus mechanism ensures consistent and trustless execution of smart contracts across the network. The EVM also manages Ethereum’s state, including account balances, smart contract code and data, and more.

The EVM is Turing complete, meaning it can execute any algorithm given enough time and gas. It interprets a low-level, stack-based bytecode language that is compatible with the Ethereum blockchain. Solidity smart contracts are compiled to this bytecode before execution.

The EVM also handles the internal cryptocurrency of Ethereum, known as Ether. Ether is used to pay for transaction fees, which are calculated based on the computational resources used by a transaction. This system prevents spam transactions and abuse of the network.

What is OpenZeppelin?

OpenZeppelin is a library for secure smart contract development. It provides implementations of standard contracts like ERC20 and ERC721, which can be deployed as-is or customized to suit specific needs. OpenZeppelin prioritizes security and offers a comprehensive suite of audited and tested smart contracts.

OpenZeppelin Contracts is the core library, providing reusable and audited smart contracts for Ethereum and other EVM and eWASM blockchains. It covers a wide range of functionalities, including access control, token standards, and more.

In addition to the Contracts library, OpenZeppelin offers other tools and services:

  • OpenZeppelin Defender: A platform for automating Ethereum operations, managing governance, and performing transactions.
  • OpenZeppelin Test Environment: A testing library that simplifies writing tests for Ethereum applications.
  • OpenZeppelin Upgrades: A system for managing and deploying upgradable smart contracts.

By leveraging OpenZeppelin’s suite of tools and libraries, developers can build secure and reliable blockchain applications.