Bundle Analysis

Bundle Analysis: Impact of types and libraries on bundle size.

1. Problem Statement

Case Study: ShopEase E-Commerce Platform

ShopEase is an e-commerce platform:

• The team wants blazing-fast load times for customers worldwide, especially on slow mobile networks.

• Developers have added many third-party libraries for charts, UI, and date handling, and used TypeScript for type safety.

• Recently, the bundle size has ballooned, causing slow page loads and poor SEO.

• Management asks: Which types, modules, and libraries are making our bundle so big? How can we analyze and optimize it?

  

The challenge:
How do you analyze and understand the impact of TypeScript code, types, and third-party libraries on your app’s bundle size—and what practical steps can you take to optimize it?

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2. Learning Objectives

By the end of this tutorial, you will:

• Understand what contributes to bundle size in a TypeScript/JavaScript app.

• Analyze your bundle using modern tools (Webpack Bundle Analyzer, Rsdoctor, Statoscope).

• Identify the impact of types, code, and libraries on bundle size.

• Apply strategies such as tree shaking, code splitting, and selective imports to reduce bundle size.

• Avoid common pitfalls when adding libraries or using TypeScript features.

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3. Concept Introduction with Analogy

Analogy: The ShopEase Delivery Truck

• Your app’s bundle is like a delivery truck: every file, library, and type is a package on board.

• The more you add, the heavier and slower the truck (your website) gets.

• Some packages are necessary (core features), but others are just “nice-to-have” or even duplicates.

• Bundle analysis is like opening the truck and weighing each package, so you can remove or shrink what’s unnecessary.

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4. Technical Deep Dive

A. What Affects Bundle Size?

• Your own code: The more code and features, the bigger the bundle.

• TypeScript types: Types themselves are erased at build time, but poorly configured TypeScript or unused code can still bloat your output.

• Third-party libraries: Every npm package you import is included in the bundle, unless tree shaking removes unused parts.

• Duplicate dependencies: Multiple versions of the same library can be bundled.

• Non-JS assets: Images, fonts, CSS, etc., if imported, add to bundle size.

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B. Analyzing the Bundle

1. Using Webpack Bundle Analyzer

• Install:

npm install --save-dev webpack-bundle-analyzer

• Add to your Webpack config as a plugin, or run with:

npx webpack-bundle-analyzer dist/bundle.js

• What you see:

  • A visual treemap of all modules and their sizes.

  • Which libraries (e.g., lodash, moment, chart.js) are the biggest.

  • Duplicates and unused code.

• You can also use [Rsdoctor] or [Statoscope] for deeper analysis.

2. Key Metrics

• Total bundle size: The sum of all JS, CSS, and assets.

• Initial chunk size: What’s loaded on the first page view.

• Duplicate packages: Multiple versions of the same dependency.

• Module sizes: Which files or libraries are the largest.

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C. The Impact of Types and TypeScript Features

• TypeScript types do NOT increase runtime bundle size—they are erased during compilation.

• However, TypeScript can help bundlers eliminate dead code (tree shaking) by making unused exports easier to detect.

• Excessive or unnecessary type annotations do not affect bundle size, but importing large type declaration files (from huge libraries) can slow down builds.

• TypeScript features like enums or decorators may generate extra JavaScript code, increasing bundle size slightly.

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D. The Impact of Libraries

• Every library you import adds to the bundle. Some, like lodash or moment, are very large.

• Importing the whole library:

import _ from 'lodash'; // BAD: includes all of lodash

• Importing only what you need:

import debounce from 'lodash/debounce'; // GOOD: includes only debounce

• Tree shaking: Modern bundlers (Webpack, Rollup) remove unused exports from ES modules, but only if you use ES import/export syntax and avoid side effects.

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E. Strategies for Reducing Bundle Size

1. Analyze before you optimize:

   • Use tools like Webpack Bundle Analyzer or Rsdoctor to visualize your bundle.

2. Remove unused libraries and code:

   • Every unused import is wasted bytes.

3. Use tree-shakable libraries:

   • Prefer libraries with ES module support and no side effects.

4. Import only what you need:

   • Use direct imports for lodash, date-fns, etc.

5. Code splitting and lazy loading:

   • Load large or rarely-used features only when needed.

6. Minify and compress:

   • Use Terser, esbuild, or built-in minification.

7. Avoid duplicate dependencies:

   • Check your lockfile and dependency tree for multiple versions.

8. Optimize TypeScript config:

   • Set "module": "esnext" and "target": "es2017" or higher for better tree shaking.

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5. Step-by-Step Data Modeling & Code Walkthrough

A. Analyzing Your Bundle

npm install --save-dev webpack-bundle-analyzer npx webpack-bundle-analyzer dist/bundle.js

• Open the report and look for:

  • Large libraries (e.g., chart.js, moment, lodash)

  • Duplicates (e.g., two versions of react)

  • Your own code’s size

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B. Reducing Bundle Size: Example

Before:

import _ from 'lodash';
const result = _.debounce(fn, 300);

After:

import debounce from 'lodash/debounce';
const result = debounce(fn, 300);

The second form only includes the debounce function, not all of lodash

C. TypeScript Config for Better Bundling

// tsconfig.json
{
  "compilerOptions": {
    "module": "esnext",
    "target": "es2017",
    "moduleResolution": "node",
    "esModuleInterop": true,
    "declaration": false,
    "removeComments": true
  }
}

• This setup helps bundlers tree shake unused code and reduces output size.

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D. Minifying and Compressing

-   Use Terser or esbuild for minification:
// webpack.config.js
const TerserPlugin = require('terser-webpack-plugin');
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [new TerserPlugin()],
  },
};

• Minification removes whitespace, comments, and dead code.

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6. Interactive Challenge / Mini-Project

Your Turn!

1. Use Webpack Bundle Analyzer (or Rsdoctor/Statoscope) on your project.

2. Identify the three largest libraries in your bundle.

3. Refactor your imports to only include what’s needed (e.g., for lodash, date-fns, or moment).

4. Change your tsconfig.json to "module": "esnext" and rerun your build—does the bundle shrink?

5. Remove an unused library and rerun the analyzer—how much did you save?

6. Bonus: Add code splitting for a rarely-used admin page and compare the initial chunk size before and after.

7. Common Pitfalls & Best Practices

Common Pitfalls & Best Practices (Bundle Optimization)

Pitfall	Best Practice
Importing whole libraries	Only import needed functions/modules
Not analyzing bundle regularly	Use analyzer tools after every major change
Not leveraging tree shaking	Use ES modules and set tsconfig for ESNext
Duplicate dependencies	Deduplicate via lockfile or dependency updates
Ignoring minification	Always minify and compress for production

8. Optional: Programmer’s Workflow Checklist

• Analyze bundle after every major dependency or feature addition.

• Prefer tree-shakable, modular libraries.

• Use direct imports for utility libraries.

• Keep tsconfig optimized for bundling.

• Remove unused code and dependencies.

• Always minify and compress production builds.