My Web3 Learning Week Bridges, Cross-Chain Logic & Smart Contract Interaction
I am a software engineer with a strong background in competitive programming and backend focused development.
I graduated in IT from Army Institute of Technology, Pune (2025) and currently work at NxtWave, where I build and review technical content around data structures, algorithms, and problem solving.
My recent work is focused on smart contract and protocol development using Solidity and Foundry. I enjoy building systems where correctness, security, and clear invariants matter such as token vesting, staking mechanisms, and upgradeable protocols.
Earlier, I spent several years in competitive programming (Codeforces Expert, 5★ CodeChef), which shaped how I approach problem solving, edge cases, and testing.
On this blog, I write about the design and implementation of smart contracts, testing strategies, and engineering tradeoffs I encounter while building Web3 protocols.
For the past few days, I’ve been deep-diving into one of the most important concepts in Web3: Blockchain Bridges. Along the way, I also strengthened my Solidity fundamentals, explored ERC-20 token internals, and learned how to interact with smart contracts from both the browser and Node.js.
This article is a summary of everything I learned along with the small bridge prototype I built to connect two blockchains.
Here is the image of my bridge project
🔹 Understanding Bridges — Why We Need Them
A blockchain on its own is isolated. Ethereum cannot directly talk to Polygon, Solana, or Base. So how do assets move between chains?
That’s where bridges come in.
A typical bridge does not actually “move” your token to another blockchain. Instead, it follows a lock-and-mint mechanism:
Lock tokens on Chain A
Generate a proof/event
Mint or release equivalent tokens on Chain B
The real token never leaves its original chain — only its “representation” moves across networks.
This simple idea powers almost all cross-chain asset transfers today.
🔹 Building a Lock Contract (Custom ERC-20 Token)
The first part of my implementation was creating a simple lock contract for an ERC-20 token.
The lock contract’s responsibilities:
Accept tokens from the user
Store (lock) them inside the contract
Emit an event that validators/relayers can listen to
Allow the bridge on the destination chain to mint/release tokens based on this event
This helped me understand why events are so important in blockchain development — they act as signals for off-chain processes.
🔹 Diving Deeper into Solidity
During the lectures, I reviewed and applied several Solidity fundamentals:
✔️ ABIs & Bytecode
Understanding how the compiler converts Solidity into low-level code that the EVM executes.
✔️ Contract Structure
pragma, contract, constructors, functions, and storage variables.
✔️ ERC-20 Token Internals
Balance mapping, allowances, transfers, decimals, mint/burn controls.
✔️ Interfaces
Writing contracts that interact with external contracts safely.
✔️ Events
Publishing on-chain data that off-chain systems can react to.
These concepts started coming together naturally once I began building the bridge.
🔹 How Bridge Contracts Actually Work
(BridgeETH, BridgeBase, and a custom example)
One of the most valuable parts of the week was reading real-world bridge implementations:
How they verify proofs
How they prevent replay attacks
How tokens are released after a lock event
How shared keys or signatures are used in cross-chain messaging
Understanding these helped me appreciate how much engineering goes into making bridges both secure and reliable.
🔹 Interacting With Contracts (Browser + Node.js)
A major highlight was learning how to interact with smart contracts through RPC:
🖥️ From the Browser
Reading on-chain data (balanceOf, totalSupply)
Writing transactions (transfer, approve)
Connecting wallets
🖧 From a Node.js Backend
Creating a wallet programmatically
Signing transactions server-side
Sending contract calls automatically
Listening for blockchain events
This skill is essential for building full-stack dApps.
🔹 Final Build: A Simple One-Way Bridge Prototype
To bring everything together, I built a minimal working bridge flow:
On Chain A:
User locks tokens
Contract emits a “Locked” event
Off-chain:
Script listens for the event
Sends a message to Chain B’s contract
On Chain B:
- Contract mints tokens to the user
This is, of course, a simplified version — but coding the flow gave me clarity on how real bridges like Wormhole, Hop, Synapse, etc., actually work.
🔗 Codebase
All the contracts and scripts I built this week are available here:
👉 GitHub: https://github.com/harshkumarrai/web3-repo/tree/master/week%208
Deploy link : https://web3-repo-756i.vercel.app/
🧠 Final Thoughts
This was one of my most insightful weeks in Web3 so far. Bridges are complex, but understanding them forces you to think across chains and across layers from Solidity to RPC to backend automation.
I’ll continue refining this prototype and eventually build a more secure, bidirectional version.