Bundle analysis and tree shaking in Vue - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is tree shaking in the context of Vue.js projects?

Tree shaking is a process that removes unused code from the final bundle, making the app smaller and faster by only including the parts of the code that are actually used.

beginner

Why is bundle analysis important in Vue.js development?

Bundle analysis helps you see what code is included in your final app bundle. It shows the size of each part so you can find and remove big or unnecessary code to improve performance.

intermediate

Which tool is commonly used for bundle analysis in Vue projects?

Webpack Bundle Analyzer is a popular tool that visualizes the size of webpack output files, helping developers understand and optimize their bundles.

intermediate

How does ES modules support tree shaking in Vue apps?

ES modules use static import/export syntax, which lets bundlers know exactly what code is used or unused. This helps bundlers remove unused parts during tree shaking.

advanced

What is a common cause of tree shaking not working properly in Vue projects?

Using CommonJS modules or dynamic imports can prevent tree shaking because bundlers cannot statically analyze which code is unused.

What does tree shaking do in a Vue.js project?

A Removes unused code from the final bundle

B Adds extra debugging information

C Increases the bundle size

D Changes the app's theme colors

Tree shaking removes unused code to reduce bundle size and improve performance.

Which tool helps visualize the size of your Vue app's bundle?

A Webpack Bundle Analyzer

B Vue Router

C Vuex

D ESLint

Webpack Bundle Analyzer shows a visual map of your bundle's contents.

Why do ES modules help with tree shaking?

A Because they support dynamic imports

B Because they use static import/export syntax

C Because they run faster in the browser

D Because they are written in JavaScript

Static import/export syntax allows bundlers to detect unused code for removal.

What can prevent tree shaking from working correctly?

A Using CSS files

B Using ES modules

C Using CommonJS modules

D Using Vue components

CommonJS modules use dynamic require calls, which bundlers cannot analyze well for tree shaking.

What is the main benefit of performing bundle analysis?

A To improve the app's color scheme

B To add new features to the app

C To change the app's layout

D To find and reduce large or unused code in the bundle

Bundle analysis helps identify code that can be optimized or removed to improve app size and speed.

Explain how tree shaking works and why it is useful in Vue.js projects.

Think about how bundlers decide what code to keep or remove.

Describe the purpose of bundle analysis and how it helps improve Vue app performance.

Imagine looking inside your app's package to see what takes up space.

Practice

1. What is the main purpose of tree shaking in a Vue project?

easy

A. To change the app's user interface

B. To remove unused code from the final bundle

C. To increase the size of the app bundle

D. To add more features automatically

Solution

1. Step 1: Understand tree shaking concept

   Tree shaking is a process that removes code not used in the app to reduce bundle size.

2. Step 2: Identify its effect on Vue projects

   In Vue, tree shaking helps make the app faster by removing unused components or functions.

3. Final Answer:

   To remove unused code from the final bundle -> Option B

4. Quick Check:

   Tree shaking = remove unused code [OK]

Hint: Tree shaking cuts unused code to shrink bundles [OK]

Common Mistakes:

• Thinking tree shaking adds features
• Believing it increases bundle size
• Confusing it with UI changes

2. Which of the following is the correct way to enable bundle analysis in a Vue CLI project?

easy

A. Add analyze: true in vue.config.js

B. Use npm run serve --analyze

C. Run vue-cli-service build --report

D. Set treeShake: false in package.json

Solution

1. Step 1: Recall Vue CLI bundle analysis command

   The Vue CLI supports bundle analysis with the --report flag during build.

2. Step 2: Check other options for correctness

   Options A, C, and D are incorrect or invalid ways to enable bundle analysis.

3. Final Answer:

   Run vue-cli-service build --report -> Option C

4. Quick Check:

   Bundle analysis command = build --report [OK]

Hint: Use --report flag with build for analysis [OK]

Common Mistakes:

• Adding unsupported config keys
• Using serve instead of build
• Disabling tree shaking by mistake

3. Given this Vue component import code, what will tree shaking do during production build?

import { ref, reactive, unusedFunc } from 'vue';

export default {
  setup() {
    const count = ref(0);
    const state = reactive({ name: 'Vue' });
    return { count, state };
  }
}

medium

A. All imports including unusedFunc are included in the bundle

B. Only unusedFunc is included, others removed

C. Tree shaking does not affect imports

D. unusedFunc is removed from the final bundle

Solution

1. Step 1: Identify used and unused imports

   The code uses ref and reactive, but unusedFunc is never used.

2. Step 2: Understand tree shaking effect

   Tree shaking removes unused imports like unusedFunc to reduce bundle size.

3. Final Answer:

   unusedFunc is removed from the final bundle -> Option D

4. Quick Check:

   Unused imports removed by tree shaking [OK]

Hint: Unused imports get removed in production build [OK]

Common Mistakes:

• Assuming all imports stay in bundle
• Thinking tree shaking removes used code
• Believing tree shaking is manual

4. You notice your Vue app bundle is larger than expected. Which of these is a likely cause related to tree shaking?

medium

A. You imported entire libraries instead of specific functions

B. You enabled production mode in build

C. You removed unused imports manually

D. You used ref and reactive properly

Solution

1. Step 1: Analyze import style impact on bundle size

   Importing whole libraries (like import * as lodash from 'lodash') prevents tree shaking from removing unused parts.

2. Step 2: Check other options for relevance

   Options B, C, and D either reduce bundle size or are unrelated to bundle size increase.

3. Final Answer:

   You imported entire libraries instead of specific functions -> Option A

4. Quick Check:

   Whole library imports block tree shaking [OK]

Hint: Import only needed parts to enable tree shaking [OK]

Common Mistakes:

• Thinking production mode increases bundle
• Believing manual removal is needed
• Ignoring import style effects

5. You want to reduce your Vue app's bundle size by removing unused components and libraries. Which combination of steps is best?

hard

A. Use dynamic imports for components and enable production build with bundle analysis

B. Import all components globally and disable production optimizations

C. Manually delete unused files without build tools

D. Use development build and avoid code splitting

Solution

1. Step 1: Use dynamic imports to load components only when needed

   This helps tree shaking and code splitting to reduce initial bundle size.

2. Step 2: Enable production build with bundle analysis

   This activates tree shaking and lets you see what code is included to optimize further.

3. Final Answer:

   Use dynamic imports for components and enable production build with bundle analysis -> Option A

4. Quick Check:

   Dynamic imports + production build = smaller bundles [OK]

Hint: Combine dynamic imports and production build for best results [OK]

Common Mistakes:

• Importing all components globally
• Disabling production optimizations
• Relying on manual file deletion