Bundle analysis and tree shaking in Vue - Step-by-Step Execution

Concept Flow - Bundle analysis and tree shaking

Start Build Process

↓

Analyze Bundle Contents

↓

Identify Unused Code

↓

Remove Dead Code (Tree Shaking)

↓

Generate Optimized Bundle

↓

Deploy or Serve Bundle

This flow shows how the build process analyzes the code bundle, removes unused parts, and creates a smaller optimized bundle.

Execution Sample

Vue

import { ref } from 'vue';
import { unusedFunc } from './utils';

const count = ref(0);

export default {
  setup() { return { count }; }
};

This Vue component imports a function that is never used, which can be removed by tree shaking during bundle analysis.

Execution Table

Step	Action	Code Analyzed	Result	Bundle Size Impact
1	Start build	All project files	Bundle created with all code	Full size
2	Analyze imports	import { ref } from 'vue'; import { unusedFunc } from './utils';	Detect unusedFunc is not used	No size change yet
3	Mark unused code	unusedFunc	Marked as dead code	Potential size reduction
4	Remove dead code	unusedFunc code	Removed from bundle	Bundle size reduced
5	Generate final bundle	Remaining code	Optimized bundle created	Smaller size
6	Deploy bundle	Optimized bundle	Bundle served to users	Faster load times

💡 Build completes with unused code removed, resulting in a smaller bundle.

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
bundleSize	Full size	Full size	Reduced size	Reduced size
unusedFunc	Included	Detected unused	Removed	Removed

Key Moments - 2 Insights

Why is unusedFunc removed even though it is imported?

Because the build process detects unusedFunc is never called or referenced in the code (see execution_table step 2 and 3), so it safely removes it to reduce bundle size.

Does tree shaking remove code used dynamically or via strings?

No, tree shaking only removes code that static analysis shows is unused. Code accessed dynamically or via strings may not be detected and thus stays in the bundle.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is unusedFunc marked as dead code?

A Step 3

B Step 2

C Step 4

D Step 5

💡 Hint

Check the 'Result' column for when unusedFunc is marked as dead code.

According to variable_tracker, what happens to bundleSize after step 4?

A It stays full size

B It increases

C It reduces

D It becomes zero

💡 Hint

Look at the bundleSize row and the value after Step 4.

If unusedFunc was used in the code, how would the execution_table change?

A Bundle size would increase at Step 5

B Step 3 would mark unusedFunc as used, not dead code

C Step 4 would remove unusedFunc anyway

D Build would fail

💡 Hint

Consider what happens if code is actually used during analysis (see Step 3).

Concept Snapshot

Bundle analysis scans your code to find what parts are used.
Tree shaking removes unused code to make bundles smaller.
Unused imports or functions not called get removed.
Smaller bundles load faster and improve app performance.
Dynamic code may not be removed automatically.
Use bundle analyzers to visualize what stays or goes.

Full Transcript

Bundle analysis and tree shaking help optimize Vue apps by removing unused code. The build process starts by analyzing all project files and imports. It detects which parts, like unused functions, are never used. These are marked as dead code and removed from the final bundle. This reduces the bundle size, making the app load faster. Variables like bundleSize shrink after dead code removal. Beginners often wonder why imported but unused code is removed; it's because static analysis shows it is never called. However, code used dynamically may not be removed. Visual quizzes help reinforce when code is marked unused and how bundle size changes. The quick snapshot summarizes the key points for easy recall.