This content originally appeared on DEV Community and was authored by Iz Mroen
When building modern web applications, your project usually contains many files:
- JavaScript modules (app.js, utils.js, etc.)
- Stylesheets (styles.css)
- Assets (images, fonts, etc.)
- External libraries (React, Lodash, etc.)
The browser doesn’t always understand how to handle these files directly, especially with modern ES6 imports and dependencies.
That’s where a bundler comes in.
A JavaScript bundler is a tool that takes all your code and dependencies and combines them into one (or a few) optimized files that the browser can easily load.
How does a bundler work?
- You define an entry point (for example index.js).
- The bundler looks at all the import statements and builds a dependency graph.
- It collects everything your app needs: JavaScript, CSS, images, etc.
- Finally, it outputs a bundle file (e.g. bundle.js) that the browser can run.
Why use a bundler?
- Performance: Fewer requests → faster loading.
- Compatibility: Converts modern JS (ES6+) into code older browsers can run.
- Optimization: Minifies code, removes unused code (tree-shaking).
- Developer Experience: Supports hot reloading, dev servers, and more.
⚡ Example: Vite
Vite is one of the most popular modern bundlers.
- During development, Vite uses native ES modules in the browser for speed.
- For production, it bundles your code with Rollup (another bundler).
Example project with Vite
# Create a new Vite project
npm create vite@latest my-app
cd my-app
npm install
npm run dev
-
npm run devstarts a lightning-fast dev server. -
npm run buildbundles your project into optimized static files ready for deployment.
In short
A JavaScript bundler is like a packaging machine — it gathers all the scattered pieces of your application and delivers them as a clean, optimized package to the browser.
This content originally appeared on DEV Community and was authored by Iz Mroen
Iz Mroen | Sciencx (2025-09-25T12:08:10+00:00) What is a JavaScript Bundler?. Retrieved from https://www.scien.cx/2025/09/25/what-is-a-javascript-bundler/
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