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Building a Web3 API for ERC-20 Token Balances in Minutes 🔗💸


Ever wondered how to effortlessly fetch ERC-20 token balances using a simple API? In this post, we'll dive into the journey of creating a Web3 API in just a few minutes. Whether you're a blockchain enthusiast or a developer looking to explore the world of decentralized finance, this project is a fantastic starting point.

Our goal was to streamline the process of retrieving ERC-20 token balances by creating a user-friendly API. Whether you're checking your own balance or building a wallet application, our Web3 API provides a seamless solution.

Technology Stack
We leveraged the power of two robust technologies:

Express.js: A fast, unopinionated, minimalist web framework for Node.js.
ethers.js: A JavaScript library for interacting with the Ethereum blockchain.
ERC-20 Token Contract Deployment
We kicked off the project by deploying an ERC-20 token contract on the Ethereum blockchain. This step is crucial for creating a fungible token with standardized behavior.

Project Structure
With our project folder in place, we installed Express.js and ethers.js to lay the foundation for our Web3 API. Organizing the project structure is key to maintaining a clean and scalable codebase.

Script for Token Balance Retrieval
The heart of our API lies in the script that connects to the deployed ERC-20 token contract using ethers.js. This script allows us to fetch token balances for any Ethereum wallet address.

Web3 API with Express.js
We utilized Express.js to set up a web server that exposes a user-friendly API endpoint. The server seamlessly interacts with the Ethereum blockchain, making it easy for clients to query and retrieve token balances.

API Endpoint Description
Our API endpoint is designed with simplicity in mind. By providing a wallet address as input, clients can receive detailed information about the token balance, empowering developers to integrate this functionality into their applications effortlessly.

Security Considerations
Ensuring the security of our API is paramount. We implemented robust security measures, including input validation and rate limiting, to safeguard against potential vulnerabilities.

Deployment Process
Deploying the ERC-20 token contract and starting the Express.js server were straightforward processes. We encountered and overcame challenges, providing valuable insights for anyone embarking on a similar journey.

Source Code

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

const app = express();
const port = 3000;

// Replace with your Ethereum node provider
const provider = new ethers.JsonRpcProvider('');

// Replace with your ERC-20 token contract address and ABI
const tokenContractAddress = '0x9DE45fa5fCB3481e91753f2F92889789b7ba64FD';
const tokenContractABI = [];

app.get('/balance/:address', async (req, res) => {
  try {
    const address = req.params.address;

    // Create a contract instance
    const contract = new ethers.Contract(tokenContractAddress, tokenContractABI, provider);

    // Get the balance of the provided address
    const balance = await contract.balanceOf(address);

    res.json({ address, balance: balance.toString() });
  } catch (error) {
    res.status(500).json({ error: 'Internal Server Error' });

app.listen(port, () => {
  console.log(`Server is running on port ${port}`);

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In just a few minutes, we've built a powerful Web3 API for fetching ERC-20 token balances. Whether you're a blockchain novice or an experienced developer, this project serves as a stepping stone into the exciting world of decentralized applications. Get ready to supercharge your projects with seamless blockchain interactions!

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