Bundle size analysis in Angular

Introduction

Bundle size analysis helps you see how big your Angular app files are. Smaller bundles load faster and make users happy.

When your app feels slow to load in the browser.

Before releasing a new version to check if new code made the app bigger.

To find large libraries or code parts that can be removed or optimized.

When you want to improve your app's performance and user experience.

Syntax

Angular

ng build --stats-json

# Then use a tool like 'source-map-explorer' to analyze
npx source-map-explorer dist/project-name/main.*.js

Run ng build --stats-json to create a stats file for analysis.

Use tools like source-map-explorer or webpack-bundle-analyzer to visualize bundle contents.

Examples

This command builds your Angular app and creates a stats.json file in the dist/project-name folder.

Angular

ng build --stats-json

This command opens a visual report showing which files and libraries take up space in your main bundle.

Angular

npx source-map-explorer dist/my-app/main.*.js

Use this to start a server showing an interactive bundle size report from the stats file.

Angular

npm install -g webpack-bundle-analyzer
webpack-bundle-analyzer dist/my-app/stats.json

Sample Program

This example shows the commands you run in your terminal to generate and view the bundle size report.

You do not write code inside Angular files for this; it is a build and analysis step.

Angular

/* Steps to analyze bundle size in Angular */

// 1. Build the app with stats
// Run in terminal:
// ng build --stats-json

// 2. Analyze with source-map-explorer
// Run in terminal:
// npx source-map-explorer dist/my-app/main.*.js

// This opens a browser window showing bundle size breakdown.

Important Notes

Always analyze bundle size after adding new libraries to catch big increases early.

Lazy loading modules in Angular can reduce initial bundle size and improve load speed.

Use ng build --prod for production builds to get accurate bundle sizes with optimizations.

Summary

Bundle size analysis helps find what makes your Angular app big.

Use ng build --stats-json and tools like source-map-explorer to see details.

Smaller bundles mean faster loading and better user experience.

Practice

1. What is the main purpose of bundle size analysis in Angular applications?

easy

A. To change the app's color scheme

B. To add more features to the Angular app

C. To find which parts of the app make the bundle large

D. To increase the app's loading time

Solution

1. Step 1: Understand bundle size analysis goal

   Bundle size analysis helps identify what parts of the app increase the size of the final build.

2. Step 2: Match purpose with options

   Only To find which parts of the app make the bundle large correctly states the purpose as finding large parts in the bundle.

3. Final Answer:

   To find which parts of the app make the bundle large -> Option C

4. Quick Check:

   Bundle size analysis = find large parts [OK]

Hint: Think: Why check bundle size? To find big parts [OK]

Common Mistakes:

• Confusing bundle size analysis with adding features
• Thinking it changes app appearance
• Assuming it slows down the app

2. Which Angular CLI command generates a JSON file useful for bundle size analysis?

easy

A. ng build --stats-json

B. ng serve --stats-json

C. ng test --stats-json

D. ng lint --stats-json

Solution

1. Step 1: Recall Angular CLI commands for building

   The command to build the app and generate stats is ng build --stats-json.

2. Step 2: Identify correct option

   ng build --stats-json matches the correct command to create the JSON file for bundle analysis.

3. Final Answer:

   ng build --stats-json -> Option A

4. Quick Check:

   Build with stats JSON = ng build --stats-json [OK]

Hint: Build command with --stats-json creates analysis file [OK]

Common Mistakes:

• Using ng serve instead of ng build
• Confusing test or lint commands with build
• Forgetting to add --stats-json flag

3. After running ng build --stats-json, you use source-map-explorer on the generated JSON. What will you see?

medium

A. A list of unused CSS styles

B. A list of errors in your Angular code

C. A report of unit test results

D. A visual map showing which files contribute most to bundle size

Solution

1. Step 1: Understand what source-map-explorer does

   This tool shows a visual breakdown of the bundle, highlighting file sizes.

2. Step 2: Match output with options

   A visual map showing which files contribute most to bundle size correctly describes the visual map of file size contributions.

3. Final Answer:

   A visual map showing which files contribute most to bundle size -> Option D

4. Quick Check:

   source-map-explorer output = visual size map [OK]

Hint: source-map-explorer shows visual file size map [OK]

Common Mistakes:

• Thinking it shows code errors
• Confusing with test reports
• Expecting CSS style reports

4. You ran ng build --stats-json but source-map-explorer shows no data. What is the likely cause?

medium

A. You did not generate the stats JSON file during build

B. You forgot to install source-map-explorer globally

C. You ran ng serve instead of ng build

D. Your Angular app has no components

Solution

1. Step 1: Check if stats JSON file was created

   source-map-explorer needs the stats JSON file generated by ng build --stats-json.

2. Step 2: Identify missing stats JSON as cause

   If the file is missing, source-map-explorer shows no data. This matches You did not generate the stats JSON file during build.

3. Final Answer:

   You did not generate the stats JSON file during build -> Option A

4. Quick Check:

   No stats JSON = no data in explorer [OK]

Hint: Check if stats JSON file exists before using explorer [OK]

Common Mistakes:

• Assuming source-map-explorer must be global
• Confusing ng serve with ng build
• Thinking app components affect stats generation

5. You notice your Angular bundle is very large. Which combination of actions will best reduce the bundle size?

hard

A. Disable Ahead-of-Time compilation and enable source maps

B. Use lazy loading for modules and remove unused imports

C. Add more third-party libraries and increase polyfills

D. Increase the number of components and services

Solution

1. Step 1: Identify techniques to reduce bundle size

   Lazy loading loads modules only when needed, and removing unused imports cuts unnecessary code.

2. Step 2: Evaluate options for reducing size

   Use lazy loading for modules and remove unused imports correctly combines these effective methods. Other options add size or disable optimizations.

3. Final Answer:

   Use lazy loading for modules and remove unused imports -> Option B

4. Quick Check:

   Lazy loading + clean imports = smaller bundle [OK]

Hint: Lazy load and clean imports to shrink bundle [OK]

Common Mistakes:

• Adding more libraries increases size
• Disabling AOT slows app and increases size
• Adding components without optimization