Building a basic API with Node.js and Express

Anton Ioffe - November 4th 2023 - 9 minutes read

In this comprehensive and hands-on guide, we delve into the ins and outs of building a basic yet powerful API using Node.js and Express. Reach deep into the heart of these critical web technologies as we set up a Node.js and Express project from scratch, conjure Express routes for performing CRUD operations, harness the power of Express middleware for data validation and error handling, and connect our application to a database. Peppered with practical code snippets and clear explanations, this article will empower you to create a robust API, setting a firm foundation for your future web development projects. Dive in, and let's bring this API to life.

Understanding the Basics of Node.js and Express in API Development

Node.js is an open-source, cross-platform runtime environment that offers the boon of executing JavaScript codes outside a web browser. It plays a critical role in server-side web application development, particularly in the creation of RESTful APIs. One of the striking characteristics and advantages of Node.js is its compatibility with the Representational State Transfer (REST) style. REST is a technological standard that regulates how clients and servers communicate. Node.js leverages its non-blocking, event-driven servers very well due to its single-threaded nature. This is another significant benefit when considering it for constructing REST APIs. Uniting these advantages, Developers get an edge, as they use a single language, JavaScript, for both client-side and server-side development, thereby fostering consistency and efficiency during the development process.

Express.js, another cornerstone in building a basic API, is a highly customizable HTTP server library that simplifies server setup and abstracts a lot of boilerplate associated with API development. This results in the quick creation of prototype APIs without sacrificing customization. Moreover, Express.js excels by making common web server tasks simpler, effectively earning its reputation as a staple component when building a Node.js REST API backend.

Express.js shines brightly because of its middleware and routing capabilities. To illustrate, consider an Express.js middleware function that processes incoming requests. As requests travel through the middleware 'pipeline', each function has the power to either end the request-response cycle or pass to the next function, facilitating capabilities like logging, authentication, or authorization.

In conclusion, the fusion of Node.js and Express.js provides an agile, efficient, and potent platform for building REST APIs. This technology pair enables developers to construct robust, scalable, and maintainable web services, which contributes to their popularity in modern web development. Reflect on the features and benefits of Node.js and Express.js in web service development. Have you identified any unique benefits, challenges, or intriguing uses offered by these technologies when developing APIs?

Setting up a Node.js and Express Project

To start your Node.js and Express project, firstly, establish a new project directory by running the command mkdir projectName in your terminal. Replace "projectName" with your chosen project name. Following this, utilize the command cd projectName to navigate into your newly created directory.

With your project directory ready to go, kickstart a new application by running npm init in your terminal. This will launch a step-by-step procedure requesting information such as the project's name, version, description and more. If you feel it's unnecessary, you can bypass these prompts by accepting the default values with the Enter key, or you can customize them to your liking. This whole process results in the production of a package.json file, which houses all the essential application metadata, such as details pertinent to your project, how your project should be run, and a catalogue of dependencies.

Upon setting up your project skeleton, proceed to install Express - the backbone of our application, and other necessary dependencies. To install Express, execute the command npm install express in the terminal. Should your API require additional dependencies, install them along with Express by including their names separated by spaces after the npm install command.

After the successful installation of Express, initiate application configuration by creating a new file named app.js in your project's root directory. Import Express into this file using const express = require('express');. Subsequently, set up Express and program your app to parse incoming requests with JSON payloads by adding the code below into your app.js file:

const app = express();

With these vital steps completed, your Node.js and Express API setup is well underway. Stay tuned as we proceed to map out the further steps necessary for building your API in the following sections.

Building Express Routes for CRUD Operations

Using Express.js, we can create routes for CRUD operations by linking HTTP methods with corresponding functions. Let's start with the following code examples for each CRUD operation and see how they tie together:

POST:'/resource', (req, res) => {
    // Your logic for creating a new resource
    res.send('POST to resource');

This code shows how to use to create data in an API. Ideally, you might connect with a database, parse the request data, and add a new entry to a particular data table.


router.get('/resource', (req, res) => {
    // Your logic to fetch a list of resources
    res.send('GET on resource');

In this piece, we use router.get() for reading data. In a practical sense, you'd use this function to request data from your database and return it as a response.


router.put('/resource/:id', (req, res) => {
    // Your logic for updating a specific resource
    res.send('PUT on resource/:id');

To update resource with PUT, the whole resource instance is replaced in the database. With PATCH, however, only the provided fields are updated. Always ensure that you're using the right method for the right purpose.


router.delete('/resource/:id', (req, res) => {
    // Your logic for deleting a specific resource
    res.send('DELETE on resource/:id');

Here, when you use router.delete(), the specified resource is removed from the database assuming you provided the specific 'id'.

It's crucial to comprehend the semantics of each HTTP method while creating the Express routes for CRUD operations. For instance, it's a common mistake to misuse POST and PUT interchangeably or incorrectly use GET to update or delete a resource. To avoid this error, always ensure that you're following their standard uses: POST for creating, GET for reading, PUT and PATCH for updating, and DELETE for deleting resources.

In a large-scale application, catering to thousands of URI endpoints can be overwhelming. One solution could be to modularize your routes, breaking them down into smaller, more manageable batches, each with a dedicated router instance. You could also apply autoscaling techniques to adjust resources as per the demand, and implement load balancing to distribute network traffic efficiently across multiple servers. These strategies can help maintain performance and availability as your API grows.

Implementing Middleware in Express for Data Validation and Error Handling

As an Express.js application grows more complex, one potentially beneficial structure you could introduce is using middleware for data validation and error handling. Middleware in Express.js act as 'middle-extensions' serving between the web server and your routes, processing incoming requests before they reach their designated endpoint. This tier of abstraction can be leveraged particularly in tasks of data validation and error management, enabling cleaner code and increased modularity.

The common practice when working with user-end data is validating the inputs before they pass into your application. This 'validation middleware' could take the form of simple checks, ensuring the incoming data align with the expected structure and types. For instance, in a POST route requiring a username and password, the middleware could look something like this:

function validateUserCredentials(req, res, next) {
    const { username, password } = req.body;
    if (typeof username !== 'string' || typeof password !== 'string') {
        return res.status(400).json({ error: 'Invalid user credentials format' });
}'/user', validateUserCredentials, (req, res) => {
    // User creation logic goes here

In the above example, the validateUserCredentials function is invoked before the request handler. It checks if both username and password are string values, returning an error response if not. Only once this function invokes next(), the subsequent route handler is triggered.

The second aspect, error handling, can be accommodated through an error-handling middleware. A typical Express app can contain several routes and function calls, each susceptible to throw an error. Instead of handling each error individually within the route, this task can be offloaded to a middleware dedicated to detecting and managing errors. Expanding on the previous example:

function validateUserCredentials(req, res, next) {
    const { username, password } = req.body;
    if (typeof username !== 'string' || typeof password !== 'string') {
        return next(new Error('Invalid user credentials format'));

function errorHandler(err, req, res, next) {
    return res.status(500).json({ error: err.message });
}'/user', validateUserCredentials, (req, res) => {
    // User creation logic goes here
}, errorHandler);

In this implementation, if the validation middleware encounters an error, it creates and passes the error to the next() function. This error then gets passed along the middleware chain, until it eventually hits the errorHandler. This latter function determines the response in the event of an error, which could involve logging errors, sending responses to the user, or shutting down the server. Implementing Express middleware, both for data validation and error handling, is one strategy to ensure code is more robust, modular, and readily maintainable.

In your own Express application, where might middleware implementation make the code cleaner and more efficient? Can you think of other uses of middleware aside from validation and error handling? These are just scratching the surface of the potential of middleware in Express.js.

Connecting the Express App to a Database

After successfully building the Express application, let's get it connected to a MongoDB database. MongoDB, a popular choice among Node.js developers, uses a flexible document data model, which aligns well with Node.js applications. To get started, ensure that a package known as mongodb-memory-server is installed in your setup. If not, install it by running npm install mongodb-memory-server.

First, incorporate the mongoose module into your project. Mongoose facilitates a seamless interaction with MongoDB. To install mongoose, use the command npm install mongoose. Following installation, import it into the application's main script (usually index.js or app.js) using the code snippet const mongoose = require('mongoose');. Mongoose essentially provides an interface to interact with your MongoDB data. It offers schema validation and handles the translation between objects in code and their representation in MongoDB.

After setting up Mongoose, establish a connection to the database. This involves using mongoose.connect() function which requires a connection string. A connection string, essentially an address to your MongoDB instance, is a combination of hostname, database name, and authentication information. Here's an example of a connection string mongodb://localhost:27017/mydatabase, where localhost is the hostname, 27017 the default MongoDB port and mydatabase the database name. After successfully creating a connection, ensure that you handle possible database errors and confirm a successful connection by setting up event listeners on database.on('error') and database.once('connected').

Next, let's focus on managing the collected data. Use app.use(express.json()); within the main script of the Express application to tell the app to parse incoming JSON requests. This function, acting as middleware, converts raw incoming requests into JSON, providing a convenient way to handle data within our routes.

// Connecting to MongoDB

const database = mongoose.connection;
database.on('error', (error) => console.log(error));
database.once('connected', () => console.log('Connected to database'));

// Parsing incoming JSON requests
const app = express();

To ensure the optimal operation of your application, always close the database connection when the application stops running. Doing this helps to prevent data loss or corruption and ensuring that the session closes successfully. Monitor and optimize the performance of your database operations, with strategies such as caching or indexing, to ensure high-speed and efficient data handling.


This article explores the process of building a basic API using Node.js and Express. It covers the basics of Node.js and Express, setting up a project, building CRUD routes, implementing middleware for data validation and error handling, and connecting the Express app to a database. Key takeaways include the advantages of using Node.js and Express for API development, the importance of understanding HTTP methods for CRUD operations, and the benefits of using middleware for data validation and error handling. A challenging technical task for the reader would be to create a custom middleware function in Express that performs authentication or authorization before allowing access to certain routes.