Intro to Web3.js : A Deep Dive for Web Developers

Intro to Web3.js : A Deep Dive for Web Developers


6 min read


The rise of blockchain technology has fundamentally changed how we interact with the web, It has ushered in a new era. An era of technology tailored towards decentralization and data ownership which opens up exciting possibilities for developers.

This article serves as your guide to web3.js, a powerful JavaScript library that empowers you to build Decentralized Applications (DApps) across any platform the internet can access.

What is web3.js?

web3.js is an open-source Javascript/Typescript library for interacting with the Ethereum virtual machine (EVM). The web3.js library is maintained by ChainSafe and was awarded a grant from the Ethereum Foundation in 2020 to further its development.

Web3.js empowers developers to build applications through its in-built functions and utilities for interacting with the Ethereum blockchain and other EVM-compatible blockchains.

Think of it as a toolbox filled with functions that allow your client-side application to communicate seamlessly with the blockchain. With web3.js, your application can perform actions like:

  • Sending Ether between accounts

  • Reading and writing data on the blockchain

  • Subscribing to events on the blockchain and a lot more.

These are just a few examples of the extensive capabilities provided by web3.js.

What are the core structures of Web3.js

To foster interaction with the blockchain, these core structures are important

1. Providers:

Providers act as intermediaries to the network request your application makes to the blockchain. Think of it as underwater cables that span across the world to connect your computer to the World Wide Web, only this time the provider connects you to the vast network of nodes hosting the blockchain.

There are different types of providers, each with its advantages:

  1. WebSocket Providers: This type of provider offers real-time updates on blockchain activity. It is ideal for applications that require constant monitoring ( e.g. an application that subscribes to a blockchain event).

  2. JSON-RPC Providers: This provider communicates using JSON-RPC requests. It is suitable for general interaction and data retrieval. Examples of this type of provider are Infura, Alchemy, and self-hosted nodes.

  3. HTTP/HTTPS Providers: This provider is Similar to JSON-RPC providers but it uses HTTP/HTTPS requests. It is commonly used for browser-based application

2. Smart Contracts:

In simple terms, Smart contracts are self-executing programs deployed on a blockchain. A smart contract defines a set of rules and logic that dictates how data is stored and manipulated.

This data could be data within its rules, an input, or even data already existing on the blockchain network. To interact with the program in a smart contract, you need its address on the blockchain.

web3.js library provides functionalities to:

  • Deploy Smart Contracts (although deployment often involves additional steps like compilation)

  • Interact with Deployed Contract: web3.js allows you to call functions, send transactions, and read data stored within the smart contract

3. ABIs (Application Binary Interface):

A Smart Contract ABI is the bridge between the web3.js functions and the smart contract. It defines the function, events, and variables within a smart contract. It specifies their names, parameters, and return types.

When you interact with a smart contract function using web3.js, you need to provide the function name and parameter according to the ABI definition of the smart contract

Every ABI is unique to its contract and an altercation to the smart contract results in a new ABI. It is usually generated after compilation which is very helpful for detecting syntax errors before the contract is deployed

There are two ways to obtain an ABI:

    • Generated ABI: When you compile a smart contract using tools like Solidity compiler, an ABI file is usually generated alongside the compiled bytecode.

      • Manual ABI: If you're interacting with an existing contract deployed on the blockchain, you might need to find its ABI on platforms like Etherscan or from the contract's documentation.


Use Cases for web3.js:

Here's a breakdown of some key use cases of the web3.js library:

1. Smart Contract Interaction:

  • Function Calls: Web3.js allows you to call functions defined within smart contracts. This enables your Decentralized Application (DApp) to trigger actions on the blockchain, such as:

    • Transferring tokens or cryptocurrencies between accounts.

    • Executing complex logic programmed within the contract.

    • Updating data stored on the blockchain through the contract.

2. Data Fetching:

  • Read Operations: Web3.js enabled you to retrieve data stored on the blockchain like:

    • The current value of a state variable in the smart contract.

    • Accessing historical transaction data.

    • Querying on-chain events data emitted by smart contracts.

    • Interacting with Decentralized Autonomous Organizations (DAOs) to fetch governance data or proposals.

3. On-chain Event Listen:

  • Real-time Updates: Web3.js provides mechanisms to listen for events emitted by smart contracts. This allows your DApp to react to specific blockchain activities in real-time, such as:

    • Detecting when a token transfer occurs.

    • Identifying changes in a contract's state variables.

    • Monitoring voting results in a DAO or other decentralized system.

    • Building applications that require immediate responses to on-chain events.

4. Web3.js Accounts:

Web3.js account package contains various utility functions that simplify working with Ethereum accounts. It allows for :

  • Account Management: Create, manage, and interact with Ethereum accounts.

  • Transaction Signing and Sending: Securely sign and broadcast transactions to the blockchain network.

5. Web3.js Utilities:

Web3.js offers various utility functions that simplify blockchain development, including:

  • Cryptographic Operations: Perform cryptographic operations like hashing and key generation for secure interactions.

Read more on web3.js utilities

Beyond these core use cases, web3.js empowers developers to build innovative DApps across various domains, such as:

  • Decentralized Finance (DeFi): Building lending, borrowing, and exchange protocols on the blockchain.

  • Supply Chain Management: Tracking and verifying the movement of goods through the supply chain.

  • Non-Fungible Tokens (NFTs): Creating, managing, and trading NFTs representing unique digital assets and real-world assets.

  • Decentralized Marketplaces: Enabling peer-to-peer marketplaces without intermediaries.

  • Decentralized Games (DApps): Building games that leverage blockchain technology for secure ownership and in-game economies.


The world of web3.js is vast and brimming with potential. This article has equipped you with the foundational knowledge to embark on your journey as a web3 developer. But this is just the beginning!

Your next stop - The comprehensive web3.js course Web3.js v4 Course

For a deeper dive into web3.js functions and utilities, head over to the Official Web3.js Documentation and the ChainSafe blog. Here, you'll find a treasure trove of resources, including:

  • Detailed tutorials: Step-by-step guides that walk you through building real-world DApps with web3.js.

  • Advanced use cases: Plugins and third-party packages utilizing web3.js under the hood.

  • Expert insights: The documentation and chainsafe blog is constantly updated with valuable knowledge from industry professionals who are shaping the future of web3 development.