What is Node.js?
Node.js is a powerful JavaScript runtime environment that allows JavaScript to run outside the browser, specifically on the server side.
Originally, JavaScript was designed to manipulate the DOM (Document Object Model) in web browsers. It was used to dynamically change elements on a webpage — for example, modifying a button’s color on hover, updating text, or adjusting font size.
However, JavaScript was not initially intended for server-side programming.
That changed with the creation of Node.js, which was built on Google’s V8 JavaScript engine. The V8 engine compiles JavaScript directly into machine code, making it incredibly fast and efficient. By leveraging V8, Node.js enables developers to write server-side logic using JavaScript — something that wasn’t possible before.
This innovation opened the door to full-stack JavaScript development, where you can use a single language — JavaScript — for both the frontend and backend of an application.
How Node.js & Express.js Work Together
Client Side (App or Browser)
When a client (such as a browser or mobile app) sends a request to the server — for example, to log in — that request is handled by a backend built with Node.js.
What is Expressjs
Express.js is a lightweight and flexible Node.js framework that simplifies the process of handling HTTP requests, routing, and building APIs.
While Node.js provides the runtime, Express.js adds structure and tools that make it easier to build and manage web servers.
It acts as a bridge between Node.js and the client, making it easier to:
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Handle routes (GET, POST, etc.)
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Parse incoming request data
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Manage responses
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Connect to databases
Example: User Login Flow
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The client sends a login request to the server (built with Node.js and Express.js).
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The server receives this request via Express and forwards it to the database to check if the provided username and password match an existing user.
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Based on the database response:
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❌ If the user does not exist, the server sends a response back to the client saying: “User not found.”
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✅ If the user exists but the password is incorrect, the server responds with a validation error: “Incorrect password.”
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✅ If both the username and password are correct, the server sends back the user data or a success message to the client.
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Express handles this entire process smoothly, ensuring each part — from routing to response — works efficiently.
