JavaScript Bundle Analyzer

JavaScript is the most expensive resource on the web. Unlike images, which only need to be downloaded and decoded, JavaScript must be downloaded, parsed, compiled, and executed. Large bundles are the primary cause of poor interactivity metrics and are a major focus of modern Web Performance optimization.

Bundle Size Benchmark Tool

Enter your initial JavaScript bundle size (minified and gzipped) to see how it compares to industry standards and the HTTP Archive dataset.

Strategies for Shrinking Your Bundle

1. Code Splitting

Instead of sending one massive app.js file containing every route, component, and library in your app, code splitting breaks your code into smaller chunks. Users only download what they need for the current view.

// React Example
import React, { Suspense, lazy } from 'react';

// This creates a separate JS chunk for the Settings component
const Settings = lazy(() => import('./Settings'));

function App() {
  return (
    <Suspense fallback={<Spinner />}>
      <Settings />
    </Suspense>
  );
}

2. Dynamic Imports for Heavy Libraries

Sometimes you need a massive library (like a PDF generator, complex charting tool, or rich text editor), but only when the user clicks a specific button. Do not include this in your main bundle!

button.addEventListener('click', async () => {
  // The browser only downloads the library when clicked
  const Chart = await import('chart.js/auto');

  // Initialize chart...
  new Chart.default(ctx, config);
});

3. Tree Shaking

Tree shaking is dead-code elimination. When you import a library, you often only use a fraction of its functions. A modern bundler (Webpack, Vite, ESBuild) can detect unused code and strip it from the final bundle.

import lodash from 'lodash';
const arr = lodash.compact([0, 1, false, 2, '', 3]);

import { compact } from 'lodash-es';
const arr = compact([0, 1, false, 2, '', 3]);

4. Avoid Massive Dependencies

Before installing an npm package, check its size using tools like Bundlephobia. Often, there are modern, lightweight alternatives.

• Instead of Moment.js (72KB), use date-fns (modular) or the native Intl API.
• Instead of heavy UI component libraries, consider using headless UI libraries paired with Tailwind CSS.

Analyzing Your Bundle Locally

To truly understand what is bloating your bundle, you need a visual map of your dependencies. If you use Webpack, install webpack-bundle-analyzer. It generates an interactive treemap showing exactly how many kilobytes each dependency is consuming.