Tree shaking and dead code removal in Angular - Performance & Optimization

Performance: Tree shaking and dead code removal

HIGH IMPACT

This affects the bundle size and initial load speed by removing unused code from the final app package.

Including only necessary code in the Angular app bundle

Angular

import { ComponentA } from 'library';
@Component({ ... })
export class MyComponent { ... }

Imports only the used component, enabling tree shaking to remove unused code.

📈 Performance Gainreduces bundle size by 80%+, speeds up initial load and LCP

Including only necessary code in the Angular app bundle

Angular

import { ComponentA, ComponentB, ComponentC } from 'library';
// Using only ComponentA in the app
@Component({ ... })
export class MyComponent { ... }

Imports all components even if only one is used, increasing bundle size unnecessarily.

📉 Performance Costadds 100kb+ to bundle, blocks rendering longer on initial load

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Import entire library	No direct impact	No direct impact	Larger JS bundle delays paint	[X] Bad
Import only used modules	No direct impact	No direct impact	Smaller JS bundle speeds paint	[OK] Good

Rendering Pipeline

Tree shaking happens during build time, reducing the JavaScript bundle size. Smaller bundles download and parse faster, improving the critical rendering path.

→Network

→JavaScript Parsing

→JavaScript Execution

⚠️ BottleneckNetwork and JavaScript Parsing stages due to large bundle size

Core Web Vital Affected

LCP

This affects the bundle size and initial load speed by removing unused code from the final app package.

Optimization Tips

1Always import only what you use to enable tree shaking.

2Use ES module syntax for static imports to help dead code removal.

3Check bundle size regularly to catch unused code increasing load time.

Performance Quiz - 3 Questions

What is the main benefit of tree shaking in Angular apps?

A Faster database queries

B Improved CSS styling performance

C Smaller JavaScript bundles leading to faster page loads

D Better image compression

DevTools: Network

How to check: Open DevTools, go to Network tab, reload page, filter by JS files, and check bundle sizes.

What to look for: Look for large JavaScript files that could be reduced by tree shaking; smaller bundles indicate better dead code removal.

Practice

1. What is the main purpose of tree shaking in Angular?

easy

A. To remove unused code and imports during the build process

B. To add extra debugging information to the app

C. To increase the size of the final bundle

D. To automatically update Angular dependencies

Solution

1. Step 1: Understand tree shaking concept

   Tree shaking is a process that removes unused code and imports from the final build.

2. Step 2: Identify its effect in Angular

   In Angular, tree shaking helps reduce app size by excluding code that is never used.

3. Final Answer:

   To remove unused code and imports during the build process -> Option A

4. Quick Check:

   Tree shaking = remove unused code [OK]

Hint: Tree shaking removes unused code to shrink app size [OK]

Common Mistakes:

• Thinking tree shaking adds code instead of removing
• Confusing tree shaking with debugging tools
• Believing tree shaking updates dependencies automatically

2. Which syntax correctly imports a module that can be tree shaken in Angular?

easy

A. import * as Component from '@angular/core';

B. import Component from '@angular/core';

C. require('@angular/core').Component;

D. import { Component } from '@angular/core';

Solution

1. Step 1: Recognize ES module import syntax

   Angular uses ES module syntax: import { NamedExport } from 'module';

2. Step 2: Identify correct import for Component

   The correct syntax is importing Component as a named export inside curly braces.

3. Final Answer:

   import { Component } from '@angular/core'; -> Option D

4. Quick Check:

   Correct ES module import = import { Component } from '@angular/core'; [OK]

Hint: Use curly braces for named imports in Angular [OK]

Common Mistakes:

• Using default import syntax for named exports
• Using CommonJS require instead of ES import
• Importing everything as a namespace unnecessarily

3. Given this Angular service code, what will be removed by tree shaking if unusedMethod() is never called anywhere?

export class DataService {
  fetchData() { return 'data'; }
  unusedMethod() { return 'not used'; }
}

medium

A. Only fetchData will be kept; unusedMethod will be removed

B. Both fetchData and unusedMethod will be kept

C. Only unusedMethod will be kept; fetchData will be removed

D. Neither method will be removed

Solution

1. Step 1: Identify used and unused methods

   fetchData is assumed used; unusedMethod is never called anywhere.

2. Step 2: Apply tree shaking effect

   Tree shaking removes unused code like unusedMethod to reduce bundle size.

3. Final Answer:

   Only fetchData will be kept; unusedMethod will be removed -> Option A

4. Quick Check:

   Unused code removed = Only fetchData will be kept; unusedMethod will be removed [OK]

Hint: Unused methods get removed by tree shaking [OK]

Common Mistakes:

• Assuming all methods stay regardless of usage
• Confusing tree shaking with runtime errors
• Thinking tree shaking removes used code

4. You notice your Angular app bundle size is large despite removing unused components. What is a likely cause related to tree shaking?

medium

A. Your code uses only arrow functions

B. You are importing entire modules instead of specific components

C. You forgot to run the production build command

D. You are using lazy loading for modules

Solution

1. Step 1: Understand tree shaking limitations

   Tree shaking works best when importing specific parts, not whole modules.

2. Step 2: Identify import style impact

   Importing entire modules prevents tree shaking from removing unused parts, increasing bundle size.

3. Final Answer:

   You are importing entire modules instead of specific components -> Option B

4. Quick Check:

   Whole module imports block tree shaking = You are importing entire modules instead of specific components [OK]

Hint: Import specific parts, not whole modules, for tree shaking [OK]

Common Mistakes:

• Ignoring production build optimizations
• Thinking arrow functions affect tree shaking
• Believing lazy loading increases bundle size

5. How can you ensure a utility function in Angular is not removed by tree shaking even if it appears unused?

hard

A. Define it inside a component class without export

B. Mark it with a special comment like /* keep */

C. Export it and use it in a component or service

D. Use it only in test files

Solution

1. Step 1: Understand tree shaking criteria

   Tree shaking removes code not referenced anywhere in the app.

2. Step 2: Prevent removal by usage

   Exporting and using the function in components or services marks it as used, so it stays.

3. Final Answer:

   Export it and use it in a component or service -> Option C

4. Quick Check:

   Used code is kept by tree shaking = Export it and use it in a component or service [OK]

Hint: Use exported functions in app code to keep them [OK]

Common Mistakes:

• Thinking comments prevent tree shaking
• Defining functions without export to keep them
• Using functions only in tests to keep them