Ether.js Crash Course Notes

Introduction to Ether.js

• Ether.js: A rapidly growing library for building Web 3.0 applications.
• Preferred by developers for its elegance and speed in creating JavaScript-based blockchain applications.

Overview of Ether.js Usage

• Target Audience: Suitable for both advanced and beginner developers.
• Goal: To provide knowledge for building blockchain applications effectively.

Web Architecture Overview

Traditional Web (Web 2.0)

• Users interact through web browsers (Chrome, Safari, etc.) with a central server.
• Frontend is developed using HTML, CSS, and JavaScript; backend is stored on a central server.

Decentralized Web (Web 3.0)

• Users interact with decentralized applications (dApps).
• Instead of a central server, the application communicates directly with a blockchain.
• Smart contracts act as the backend, with data stored on the blockchain itself.

Connecting to the Blockchain with Ether.js

• Ether.js serves as a bridge between client applications (websites, scripts, etc.) and the blockchain.
• Allows interaction with smart contracts and fetching information from the blockchain.

Setting Up a Project with Ether.js

Example Setup

1. Clone the Repository: git clone <repository-url>
2. Install Packages: Run npm install in the cloned directory.
3. Text Editor: Open the project using any text editor (e.g., Sublime Text).
4. Example Scripts: Various scripts will demonstrate using Ether.js.

First Example: Fetching Account Balance

Steps

1. Import Ether.js:

   const ethers = require('ethers');
   

2. Connect to Ethereum Node: Use a provider such as Infura.

   const provider = new ethers.providers.JsonRpcProvider('<infura-url>');
   

3. Fetch Balance:

   const balance = await provider.getBalance('<ethereum-address>');
   console.log(ethers.utils.formatEther(balance));
   

4. Async Function: Wrap in an async function to handle waits.

Interacting with Smart Contracts

Smart Contracts Overview

• Smart contracts are programs on the blockchain that can be interacted with.
• Example: Reading the DAI stablecoin contract using its ABI.

Steps to Interact with Smart Contracts

1. Setup Contract:

   const contract = new ethers.Contract(<contract-address>, <abi>, provider);
   

2. Call Functions: Use functions like contract.name() or contract.symbol() to fetch data.

Sending Transactions

Basic Ether Transactions

1. Create Wallet: Use a private key to create a wallet instance.

   const wallet = new ethers.Wallet(<private-key>, provider);
   

2. Send Transaction:

   const tx = await wallet.sendTransaction({ to: <receiver-address>, value: ethers.utils.parseEther('0.025') });
   

3. Transaction Receipt: Await for the transaction to be mined and log the receipt.

Writing to Smart Contracts

Sending Tokens Example

1. Setup Contract for Tokens:

   const tokenContract = new ethers.Contract(<token-address>, <erc20-abi>, wallet);
   

2. Transfer Tokens:

   const tx = await tokenContract.transfer(<receiver-address>, ethers.utils.parseUnits('10', 18));
   

Listening for Smart Contract Events

1. Query Contract Events:

   const filter = tokenContract.filters.Transfer();
   const events = await tokenContract.queryFilter(filter);
   console.log(events);
   

Inspecting Blockchain Blocks

1. Get Latest Block:

   const blockNumber = await provider.getBlockNumber();
   const block = await provider.getBlock(blockNumber);
   console.log(block);
   

Conclusion

• Ether.js allows developers to build decentralized applications efficiently.
• Skills gained from this course can be applied to create real-world blockchain applications.