Introduction to dApps: Creating Decentralized Apps on Ethereum

Introduction to Decentralized Applications (dApps)

Decentralized applications, or dApps, are applications that run on a decentralized network like a blockchain instead of a single centralized server. dApps have become popular with the growth of blockchain networks like Ethereum, allowing developers to create applications that utilize the benefits of decentralization.

In this tutorial, we will learn about dApps and how to develop them using Solidity for writing smart contracts and Web3.js for interacting with the Ethereum blockchain.

a diagram of a decentralized application (dApp) architecture
pic credit here

What are Decentralized Applications?

A decentralized application (dApp) is an application built on a decentralized network that combines a smart contract backend code running on a blockchain with a front-end user interface. In contrast to regular apps that are controlled by a single entity, dApps operate autonomously without a central authority.


Key properties of dApps include:

  • Open source code that runs on a decentralized blockchain network.
  • Use cryptographic tokens specific to the dApp and blockchain, such as Ether for Ethereum dApps.
  • Application data and records are stored on a public blockchain.
  • Uses a consensus mechanism like proof-of-work or proof-of-stake for validating transactions.
  • Non-custodial, meaning the users fully control their funds and accounts.

Benefits of dApps

Some key benefits of decentralized apps include:

  • Autonomous and censorship-resistant – no single entity controls the application and data.
  • Increased security due to decentralization of data.
  • Transparent operations recorded immutably on the blockchain.
  • Eliminates downtime risks associated with centralized apps.
  • Funds handled through smart contracts rather than a middleman.

Examples of dApps

Here are some examples of popular decentralized applications across various categories:

  • Finance – MakerDAO, Compound, Aave
  • Exchanges – Uniswap, PancakeSwap, Sushiswap
  • Gaming – Gods Unchained, Axie Infinity
  • Identity – Civic, uPort
  • Social Media – Steemit, Peepeth

Challenges for dApp Development

While promising, dApps also comes with some unique challenges, including:

  • Required blockchain knowledge and web3 development skills.
  • Higher development complexity compared to web apps.
  • Need for crypto wallets and tokens for users.
  • Lower speeds compared to centralized apps.
  • Difficulty achieving mainstream adoption so far.

By understanding these challenges, we can take steps to successfully develop user-friendly and mainstream dApps.

Prerequisites for dApp Development

Before we start developing decentralized apps, there are some essential skills and knowledge required.

Programming Knowledge

You need basic proficiency in web development languages like JavaScript, HTML, and CSS. Most dApp frontend code is written in JavaScript frameworks like React or Angular.

Understanding programming concepts like functions, arrays, objects, and classes is important before learning blockchain-specific languages.

Understanding Blockchain Basics

Since dApps function on blockchain networks like Ethereum, having blockchain knowledge is critical. Key concepts to learn are:

  • How public/private key encryption and digital signatures work.
  • Understanding consensus mechanisms like proof-of-work and proof-of-stake.
  • Key principles of decentralized and peer-to-peer networks.
  • How transactions are executed and recorded on a blockchain.
An image showing block chain and side chain

Learning Solidity

The most common language for writing Ethereum smart contracts is Solidity. Having a good grasp of Solidity syntax, structure, and programming patterns is essential for coding dApp backends.

Getting Familiar with Ethereum

You should have a basic understanding of Ethereum’s architecture, ecosystem, and tools like MetaMask, Remix, and Truffle before developing Ethereum dApps. Learning the differences between mainnet and testnets is also important.

Setting Up the Development Environment

Let’s look at installing the necessary tools and dependencies for building dApps on Ethereum.

Install Node.js and npm

Since dApps use JavaScript for the frontend code, install Node.js, which includes the npm package manager. Npm will be used to install JavaScript libraries and dependencies.

Install a Code Editor

You’ll need a code editor like Visual Studio Code for writing the Solidity and JavaScript code. Make sure the editor can compile, test, and debug Solidity smart contracts.


Install Truffle Framework

Truffle provides a development environment and asset pipeline for building dApps. We’ll use it for smart contract compilation, linking, deployment, and binary management.

Install Ganache

Ganache provides a local in-memory blockchain for testing dApps. This allows simulating the blockchain during development instead of needing real Ether every time.

Install MetaMask

MetaMask is a crypto wallet browser extension that allows web3 interactions with the Ethereum blockchain. We need it to connect our dApp front end with the blockchain.

Introduction to Solidity

Solidity is an object-oriented, high-level language for developing smart contracts. It is the most popular language for Ethereum dApps. Let’s learn some basics of coding in Solidity.

Structure of a Solidity Contract

A contract in Solidity encapsulates relevant data and functions that implement the logic of the program. Here is a simple contract structure:

pragma solidity ^0.8.0; 

contract SimpleStorage {

  // State variables

  // Functions

  • pragma specifies the compiler version.
  • contract defines the contract name.
  • State variables store data permanently in contracts.
  • Functions contain the logic and executable code.

Data Types

Solidity is a statically typed language, meaning data types like integers, strings, and addresses must be specified.

Some common data types are:

  • uint for unsigned integers like uint256.
  • int for signed integers.
  • address for Ethereum account addresses.
  • bool for Boolean true/false.
  • string for strings.
  • bytes for raw byte data.


Functions are the executable units of code within a contract. They allow contracts to take certain actions based on function calls.

function setNumber(uint newNumber) public {

  number = newNumber;

  • setNumber is the function name.
  • uint specifies the data type of the parameter.
  • public makes this function callable by other contracts.

Deploying and Interacting with Smart Contracts

Using tools like Remix, Truffle, and MetaMask, we can deploy contracts to testnets like Ropsten and interact with them. This allows testing the contract logic and transactions.

Introduction to Web3.js

To connect and interact with decentralized apps from the front end, we use Web3.js libraries which allow communicating with the Ethereum blockchain from JavaScript code.

Web3 js Logo
Web3 js Logo

What is Web3.js?

Web3.js is a collection of libraries that allow developers to interact with decentralized nodes from regular web apps. It acts as a bridge between the frontend code and the backend blockchain network.

Key functions provided by Web3.js include:

  • read/write data from the blockchain.
  • interact with smart contracts by sending transactions.
  • manage Ethereum accounts.
  • sign transactions cryptographically.

Connecting to Ethereum with Web3.js

To connect our app to Ethereum, first, we need to install the Web3.js npm module:

npm install web3

Then we initialize a Web3 instance and point it to a local or hosted Ethereum node using an HTTP or IPC provider:

import Web3 from 'web3';

const web3 = new Web3(window.web3.currentProvider);

Reading Blockchain Data

Web3.js provides APIs for reading network data like block number, transaction details, account balances, etc.

For example:

This prints the latest block number on Ethereum.

Writing Transactions

To write data to Ethereum, we need to create and sign transactions before sending them to the network.

Key steps are:

  1. Create a transaction object containing information like recipient, amount to send.
  2. Sign the transaction with the sender’s private key.
  3. Send the signed transaction to the network.
  4. Wait for the transaction receipt to confirm inclusion in a block.

Interacting with Smart Contracts

To call a contract function:

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

Pass the contract ABI and address to initialize a contract object.
Call the desired function using contract.methods.functionName().
Use send() to execute and send the transaction.

Developing a Simple Decentralized Application

Let’s put together the concepts learned so far by building a simple decentralized application on Ethereum.

We will build a dApp for a basic blogging platform that stores articles on the blockchain.

Defining the dApp Scope

Key features of our blogging dApp:

  • Users can register as an author by creating an account.
  • Authors can publish articles, which get added to the blockchain.
  • Articles can be edited or deleted only by the original author.
  • Users can view published articles and identify the author.

Designing the UI and UX

For the frontend interface, we can use a simple React app with a clean UX allowing easy publishing and reading of articles.

The UI can include:

  • A homepage showing published articles.
  • An editor interface for writing new articles.
  • User profiles with published articles.
  • Individual article pages.

Writing the Smart Contract

The core logic goes into the smart contract written in Solidity:

contract Blog {

  struct Article {
    uint id;
    string title;
    string content;
    address author;

  // articleId -> article mapping
  mapping (uint => Article) public articles;

  // author -> articles[] mapping
  mapping (address => Article[]) public userArticles;
  function publishArticle(string memory title, string memory content) public {
    // ...code to publish article


Key functions will include:

  • publishArticle – Adds an article to the blockchain.
  • editArticle – Edits an existing article by author.
  • getArticlesByAuthor – Retrieves articles filtered by author.

Connecting the Frontend to Smart Contract

Using Web3.js, we can initialize the contract and call functions from React:

// Initialize contract
const blogContract = new web3.eth.Contract(abi, address);

// Publish article function
const publishArticle = async (title, content) => {
  await blogContract.methods.publishArticle(title, content).send(); 

The front end will call contract functions which then execute transactions and modify contract state on Ethereum.

Testing and Deploying the dApp

Before deploying our decentralized application publicly, we need to thoroughly test it locally.


Testing Smart Contracts

For testing smart contracts, tools like Mocha, Chai, and Ganache CLI allow:

  • Setting up a local test blockchain.
  • Defining test suites and cases.
  • Checking expected vs actual outcomes.
  • Getting gas usage statistics.

Integrating Wallet

To deploy the dApp frontend, we need to integrate a crypto wallet like MetaMask with our React code.

This allows users to securely sign transactions with their private key when interacting with our dApp.

a diagram of a decentralized application (dApp) architecture with linked wallet
image is from here

Deploying on a Testnet

Initially, we can deploy the smart contracts and frontend dApp to a test network like Ropsten before mainnet.

This allows testing the entire flow end-to-end before an official production release.

Going Live on Ethereum Mainnet

Once thoroughly tested, we can deploy the contracts and frontend on the live Ethereum mainnet for public decentralized access to the dApp.

Advanced Concepts for Enhanced dApps

Let’s discuss some advanced capabilities to make decentralized apps more scalable, secure, and functional.

Implementing Event Logs

Event logs allow your smart contract to emit events that notify frontend apps when something happens, like an article getting published.

event ArticlePublished(
  uint indexed articleId, 
  address indexed author

function publishArticle(string memory title, string memory content) public {
  // ...

  emit ArticlePublished(articleId, msg.sender);

The front end can then listen for these event logs.

Using Oracle Services

Oracles allow smart contracts to fetch external data like weather data, stock prices, etc. This greatly expands the capabilities of dApps.

Decentralized Storage

For storing large amounts of data like images, decentralized storage like IPFS is better than storing directly on-chain. The hash of the IPFS data can be saved on-chain.

Securing Against Vulnerabilities

Security audits, formal verification, bug bounty programs, and secure coding practices are essential to avoid vulnerabilities in smart contracts.

a diagram showing complete architecture of a Dapp

The Future of dApps

The decentralized app ecosystem holds immense potential to disrupt many industries in the coming years.

Mainstream Adoption

As blockchain platforms like Ethereum scale and onboard millions of new users into the decentralized future of the internet, easy-to-use dApps can see huge growth in adoption across sectors.

Developer Friendliness

Frameworks and tools for dApp development will continue evolving to enhance developer experience, allowing creation of increasingly sophisticated dApps.

Evolution of Platforms

Next-generation blockchain platforms can enable faster and cheaper dApps that can rival traditional centralized applications.

Impact on Industries

Decentralized apps hold promise for revolutionizing fields like social media, finance, real estate, supply chain, healthcare, music and more. Exciting times lie ahead!

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