How To Build A Node.js API For Ethereum
Last Updated :
24 Jul, 2025
Ethereum is a popular blockchain platform that allows developers to build decentralized applications (dApps). It uses a smart contract system that enables the execution of self-executing contracts with the terms of the agreement between buyer and seller being directly written into lines of code.
The article focuses on discussing the steps to build a Node.js API for Ethereum. We will be using the Web3 library, which is a JavaScript library that allows developers to interact with the Ethereum blockchain.
Prerequisites
1. Node.js
Node.js is an open-source JavaScript runtime environment that allows developers to run JavaScript code outside of a web browser. You can download Node.js from the official website https://nodejs.org/en/download/.
2. Truffle
Truffle is a popular development framework for Ethereum that provides tools for building, testing, and deploying smart contracts. You can install Truffle using the npm package manager.
3. Ganache
Ganache is a local blockchain for Ethereum development that allows developers to test their smart contracts and dApps in a simulated environment. You can download Ganache from the official website https://archive.trufflesuite.com/ganache/.
4. Web3.js
Web3.js is a JavaScript library that allows developers to interact with the Ethereum blockchain and smart contracts using JavaScript. You can install Web3.js using the npm package manager.
5. Postman
Postman tool is used to test the API endpoint. you can download this from the official website https://www.postman.com/.
Steps to Build A Node.js API For Ethereum
Step 1: Set up a New Node.js Project
First, you need to set up a new Node.js project. Open a terminal and create a new directory for your project. Then, initialize a new Node.js project using the following command:
mkdir contracts
cd contracts
npm init
Follow the prompts to create a new Node.js project.
Step 2: Install the Required Dependencies
Next, you need to install the required dependencies for your Node.js API. Use the following commands to install Truffle and Ganache.
npm install -g truffle
npm install -g ganache
You can also download the GUI version of ganache from their official website https://archive.trufflesuite.com/ganache/ Once you have installed Ganache, open the application and click the "Quickstart" button. This will start a new blockchain with 10 accounts, each with 100 ETH.
Step 3: Create a New Truffle Project
Next, you need to create a new Truffle project. Use the following command to create a new Truffle project:
$ truffle init
This command will create a new Truffle project with the following directories:
- contracts: This directory will contain your smart contract code.
- migrations: This directory will contain your migration scripts for deploying your smart contracts.
- test: This directory will contain your test scripts for testing your smart contracts.
Here, you can see in below picture:
Create the truffle project
Now, open truffle-config.js file and uncomment the development section from the code and then save the file. Here, you can see it in the picture.
truffle-config.js fileStep 4: Write Smart Contract Code
Next, you need to write your smart contract code. Open the contracts directory and create a new file called MyContract.sol. In this file, write the smart contract code using the Solidity programming language.
Solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
//creating smart contract
contract MyContract {
uint256 private myNumber;
//defining function
function getNumber() public view returns (uint256) {
return myNumber;
}
function setNumber(uint256 _number) public {
myNumber = _number;
}
}
create smart contract
This smart contract has a public variable myNumber, and two functions setNumber and getNumber. The setNumber function sets the value of myNumber, and the getNumber function returns the value of myNumber.
Step 5: Compile Smart Contracts
Next, you need to compile your smart contracts. Use the following command to compile your smart contracts:
truffle compile
compile the smart contract
This command will compile the smart contracts and generate JSON artifacts in the build/contracts directory.
Step 6: Deploy Smart Contracts
Create a new file named 2_deploy_contracts.js in the migrations directory and add the following code:
Next, we need to deploy the smart contract to the Ethereum blockchain using Ganache CLI. To do this, open a new terminal window and run the following command
Run the following command to migrate the smart contract:
ganache-cli
ganache
This command will start a local blockchain that you can use for testing your smart contracts.
Now, back in the original terminal window, run the following command to deploy the smart contract:
truffle migrate
deploy the smart contract
This command will deploy your smart contracts to the Ganache blockchain and create a new migration script in the migrations directory. Here, we can see all the details. Next, you have to copy this contract address. You will use this while creating a Node.js API for Ethereum.
Step 7: Create your Node.js API and Integrate it into Smart Contracts
First, install all the dependencies needed for the project. Run the following command in the terminal:
npm install web3
npm install express
This will install the Express framework and the Web3.js library.
To check if it's properly installed or not go to the package.json file. and see the version of these dependencies.
package.json file
Next, you need to write the code for your Node.js API. Create a new file called app.js in the root directory of your project. In this file, you will write the code for your Node.js API.
JavaScript
const express = require('express');
const Web3 = require('web3');
const MyContract = require("./build/contracts/MyContract.json");
const contractABI = MyContract.abi;
const contractAddress = '0x12477A837422364C31fE250b50a2Aab492Ec5C0e'; // Enter your contract address here
const rpcEndpoint = 'http://127.0.0.1:8545'; // Enter your RPC server endpoint URL here
const app = express();
const web3 = new Web3(new Web3.providers.HttpProvider(rpcEndpoint));
const contract = new web3.eth.Contract(contractABI, contractAddress);
app.use(express.json());
app.get('/number', async (req, res) => {
const number = await contract.methods.getNumber().call();
res.json({ number });
});
app.post('/number', async (req, res) => {
const { number } = req.body;
const accounts = await web3.eth.getAccounts();
const result = await contract.methods.setNumber(number).send({ from: accounts[0] });
res.json({ message: 'number set successfully' });
});
app.listen(3000, () => {
console.log('Server listening on port 3000');
});
Create API code
Explanation:
In the code above, the Express and Web3 libraries, and the ABI of our smart contract are imported.
- We also define the address of our smart contract, which we got from the deployment process.
- A new instance of the Web3 class is created and passed to an HTTP provider that points to http://localhost:8545.
- We also create a new instance of the Contract class and pass it to the ABI and address our smart contract. and the contract address which was copied during the deployment process.
- Paste that contract address in the contractAddress class.
const contractAddress = '0x12477A837422364C31fE250b50a2Aab492Ec5C0e'; // Enter your contract address here
- Two API endpoints, /number GET and /number POST are defined. The GET endpoint returns the value of myNumber by calling the getNumber() function of the smart contract. The POST endpoint sets the value of myNumber by calling the setNumber() function of the smart contract.
Step 8: Test your Node.js API
To test the API, you can use a tool like Postman, which allows you to send requests to the API and view the responses.
1. Run Ganache Command: First, run the ganache command to start the local Ethereum node. So, open a new terminal and run the following command:
ganache-cli
This will start a local blockchain network with 10 accounts, each having 100 ethers.
2. Start Node.js Server: Now, back to the original terminal and start the Node.js server. run the file app.js using the command:
node app.js
Node.js server started
3. Create a GET Request: Next, open the postman to test the API request. Click on the "New" button in Postman and select "Request". In the "Request" tab, set the URL to http://localhost:3000/number, select the GET method, and click the "Send" button. You should see the value of the number in the response body.
get method to fetch data
4. Create a POST Request: Click on the "New" button in Postman and select "Request". In the "Request" tab, set the URL to http://localhost:3000/number, select the POST method, and set the body to a JSON object with the new value for the number:
{
"number": 12
}
5. Click the Send button: Click the "Send" Button and you should see a "success" message in the response body.
post method to send data
6. Verify Changes: You can now send another GET request to http://localhost:3000/number to verify that the value of a number has been updated to the new value.
verify the change
That's it! You have now tested the API using Postman. You can use this same method to test any other endpoints you add to the API.
Conclusion
Building a Node.js API for Ethereum is a great way to interact with smart contracts and build decentralized applications. With the Truffle Suite, Web3.js, and the Express framework, it's easy to get started. Follow the steps outlined in this article, and you'll have your API up and running in no time.
Similar Reads
Node.js Tutorial Node.js is a powerful, open-source, and cross-platform JavaScript runtime environment built on Chrome's V8 engine. It allows you to run JavaScript code outside the browser, making it ideal for building scalable server-side and networking applications.JavaScript was mainly used for frontend developme
4 min read
Introduction & Installation
NodeJS IntroductionNodeJS is a runtime environment for executing JavaScript outside the browser, built on the V8 JavaScript engine. It enables server-side development, supports asynchronous, event-driven programming, and efficiently handles scalable network applications. NodeJS is single-threaded, utilizing an event l
5 min read
Node.js Roadmap: A Complete GuideNode.js has become one of the most popular technologies for building modern web applications. It allows developers to use JavaScript on the server side, making it easy to create fast, scalable, and efficient applications. Whether you want to build APIs, real-time applications, or full-stack web apps
6 min read
How to Install Node.js on LinuxInstalling Node.js on a Linux-based operating system can vary slightly depending on your distribution. This guide will walk you through various methods to install Node.js and npm (Node Package Manager) on Linux, whether using Ubuntu, Debian, or other distributions.PrerequisitesA Linux System: such a
6 min read
How to Install Node.js on WindowsInstalling Node.js on Windows is a straightforward process, but it's essential to follow the right steps to ensure smooth setup and proper functioning of Node Package Manager (NPM), which is crucial for managing dependencies and packages. This guide will walk you through the official site, NVM, Wind
6 min read
How to Install NodeJS on MacOSNode.js is a popular JavaScript runtime used for building server-side applications. Itâs cross-platform and works seamlessly on macOS, Windows, and Linux systems. In this article, we'll guide you through the process of installing Node.js on your macOS system.What is Node.jsNode.js is an open-source,
6 min read
Node.js vs Browser - Top Differences That Every Developer Should KnowNode.js and Web browsers are two different but interrelated technologies in web development. JavaScript is executed in both the environment, node.js, and browser but for different use cases. Since JavaScript is the common Programming language in both, it is a huge advantage for developers to code bo
6 min read
NodeJS REPL (READ, EVAL, PRINT, LOOP)NodeJS REPL (Read-Eval-Print Loop) is an interactive shell that allows you to execute JavaScript code line-by-line and see immediate results. This tool is extremely useful for quick testing, debugging, and learning, providing a sandbox where you can experiment with JavaScript code in a NodeJS enviro
5 min read
Explain V8 engine in Node.jsThe V8 engine is one of the core components of Node.js, and understanding its role and how it works can significantly improve your understanding of how Node.js executes JavaScript code. In this article, we will discuss the V8 engineâs importance and its working in the context of Node.js.What is a V8
7 min read
Node.js Web Application ArchitectureNode.js is a JavaScript-based platform mainly used to create I/O-intensive web applications such as chat apps, multimedia streaming sites, etc. It is built on Google Chromeâs V8 JavaScript engine. Web ApplicationsA web application is software that runs on a server and is rendered by a client browser
3 min read
NodeJS Event LoopThe event loop in Node.js is a mechanism that allows asynchronous tasks to be handled efficiently without blocking the execution of other operations. It:Executes JavaScript synchronously first and then processes asynchronous operations.Delegates heavy tasks like I/O operations, timers, and network r
5 min read
Node.js Modules , Buffer & Streams
NodeJS ModulesIn NodeJS, modules play an important role in organizing, structuring, and reusing code efficiently. A module is a self-contained block of code that can be exported and imported into different parts of an application. This modular approach helps developers manage large projects, making them more scal
6 min read
What are Buffers in Node.js ?Buffers are an essential concept in Node.js, especially when working with binary data streams such as files, network protocols, or image processing. Unlike JavaScript, which is typically used to handle text-based data, Node.js provides buffers to manage raw binary data. This article delves into what
4 min read
Node.js StreamsNode.js streams are a key part of handling I/O operations efficiently. They provide a way to read or write data continuously, allowing for efficient data processing, manipulation, and transfer.\Node.js StreamsThe stream module in Node.js provides an abstraction for working with streaming data. Strea
4 min read
Node.js Asynchronous Programming
Node.js NPM
NodeJS NPMNPM (Node Package Manager) is a package manager for NodeJS modules. It helps developers manage project dependencies, scripts, and third-party libraries. By installing NodeJS on your system, NPM is automatically installed, and ready to use.It is primarily used to manage packages or modulesâthese are
6 min read
Steps to Create and Publish NPM packagesIn this article, we will learn how to develop and publish your own npm package (also called an NPM module). There are many benefits of NPM packages, some of them are listed below: Reusable codeManaging code (using versioning)Sharing code The life-cycle of an npm package takes place like below: Modu
7 min read
Introduction to NPM scriptsNPM is a Node Package Manager. It is the world's largest Software Registry. This registry contains over 800,000 code packages. Many Open-source developers use npm to share software. Many organizations also use npm to manage private development. "npm scripts" are the entries in the scripts field of t
2 min read
Node.js package.jsonThe package.json file is the heart of Node.js system. It is the manifest file of any Node.js project and contains the metadata of the project. The package.json file is the essential part to understand, learn and work with the Node.js. It is the first step to learn about development in Node.js.What d
4 min read
What is package-lock.json ?package-lock.json is a file that is generated when we try to install the node. It is generated by the Node Package Manager(npm). package-lock.json will ensure that the same versions of packages are installed. It contains the name, dependencies, and locked version of the project. It will check that s
3 min read
Node.js Deployments & Communication
Node DebuggingDebugging is an essential part of software development that helps developers identify and fix errors. This ensures that the application runs smoothly without causing errors. NodeJS is the JavaScript runtime environment that provides various debugging tools for troubleshooting the application.What is
3 min read
How to Perform Testing in Node.js ?Testing is a method to check whether the functionality of an application is the same as expected or not. It helps to ensure that the output is the same as the required output. How Testing can be done in Node.js? There are various methods by which tasting can be done in Node.js, but one of the simple
2 min read
Unit Testing of Node.js ApplicationNode.js is a widely used javascript library based on Chrome's V8 JavaScript engine for developing server-side applications in web development. Unit Testing is a software testing method where individual units/components are tested in isolation. A unit can be described as the smallest testable part of
5 min read
NODE_ENV Variables and How to Use Them ?Introduction: NODE_ENV variables are environment variables that are made popularized by the express framework. The value of this type of variable can be set dynamically depending on the environment(i.e., development/production) the program is running on. The NODE_ENV works like a flag which indicate
2 min read
Difference Between Development and Production in Node.jsIn this article, we will explore the key differences between development and production environments in Node.js. Understanding these differences is crucial for deploying and managing Node.js applications effectively. IntroductionNode.js applications can behave differently depending on whether they a
3 min read
Best Security Practices in Node.jsThe security of an application is extremely important when we build a highly scalable and big project. So in this article, we are going to discuss some of the best practices that we need to follow in Node.js projects so that there are no security issues at a later point of time. In this article, we
4 min read
Deploying Node.js ApplicationsDeploying a NodeJS application can be a smooth process with the right tools and strategies. This article will guide you through the basics of deploying NodeJS applications.To show how to deploy a NodeJS app, we are first going to create a sample application for a better understanding of the process.
5 min read
How to Build a Microservices Architecture with NodeJSMicroservices architecture allows us to break down complex applications into smaller, independently deployable services. Node.js, with its non-blocking I/O and event-driven nature, is an excellent choice for building microservices. How to Build a Microservices Architecture with NodeJS?Microservices
3 min read
Node.js with WebAssemblyWebAssembly, often abbreviated as Wasm, is a cutting-edge technology that offers a high-performance assembly-like language capable of being compiled from various programming languages such as C/C++, Rust, and AssemblyScript. This technology is widely supported by major browsers including Chrome, Fir
3 min read
Resources & Tools
Node.js Web ServerA NodeJS web server is a server built using NodeJS to handle HTTP requests and responses. Unlike traditional web servers like Apache or Nginx, which are primarily designed to give static content, NodeJS web servers can handle both static and dynamic content while supporting real-time communication.
6 min read
Node Exercises, Practice Questions and SolutionsNode Exercise: Explore interactive quizzes, track progress, and enhance coding skills with our engaging portal. Ideal for beginners and experienced developers, Level up your Node proficiency at your own pace. Start coding now! #content-iframe { width: 100%; height: 500px;} @media (max-width: 768px)
4 min read
Node.js ProjectsNode.js is one of the most popular JavaScript runtime environments widely used in the software industry for projects in different domains like web applications, real-time chat applications, RESTful APIs, microservices, and more due to its high performance, scalability, non-blocking I/O, and many oth
9 min read
NodeJS Interview Questions and AnswersNodeJS is one of the most popular runtime environments, known for its efficiency, scalability, and ability to handle asynchronous operations. It is built on Chromeâs V8 JavaScript engine for executing JavaScript code outside of a browser. It is extensively used by top companies such as LinkedIn, Net
15+ min read