Refactoring Skill

This skill helps identify code smells and apply refactoring techniques to improve code quality. The foundational principles are from Refactoring.guru, adapted for Chrome Extension projects using Vanilla JS, Modules, and Side Panel architecture.

Core Principles

1. Clean Code: Easy to read, understand, and maintain.
2. Dirty Code: Full of "smells", difficult to maintain and extend.
3. Baby Steps: Make one small change at a time, ensuring tests pass.

Process

1. Identify Smells: Observe the code and find characteristics matching "Code Smells".
2. Select Technique: Choose an appropriate refactoring technique based on the smell type.
3. Refactor: Modify the code.
4. Verify: Ensure functionality is not affected (Manual Test / Unit Test).

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Common Code Smells and Solutions

1. Bloaters

Code, methods, or classes that have grown too large to manage.

• Long Method

  • Symptoms: A function exceeds 30-50 lines, or contains multiple levels of nesting.
  • Solution: Extract Method. Move partial logic to a new function.
  • Project Context: Large event listeners in sidepanel.js, or render() functions.

• Large Class / Module

  • Symptoms: A file (e.g., modules/uiManager.js) takes on too many responsibilities.
  • Solution: Extract Class/Module. Split by functionality.

• Long Parameter List

  • Symptoms: A function receives more than 3-4 parameters.
  • Solution: Introduce Parameter Object. Pass an Object configuration.

2. Object-Orientation Abusers

Incorrect application of OO principles.

• Switch Statements
  • Symptoms: Complex switch or if-else chains used to determine types and execute different logic.
  • Solution: Replace Conditional with Polymorphism. In Vanilla JS, use Object Map or Strategy Pattern.

3. Change Preventers

Changing one place requires changing multiple places.

• Shotgun Surgery
  • Symptoms: Every small feature addition requires modifying 5-6 files.
  • Solution: Move Method/Field. Consolidate related logic into a single module.

4. Dispensables

Useless or redundant code.

• Comments
  • Symptoms: Using comments to explain "what the code does" (instead of "why it does it").
  • Solution: Rename Method/Variable. Let the code be self-explanatory.
• Duplicate Code
  • Symptoms: Same logic appears in two or more places.
  • Solution: Extract Method and share.
  • Project Context: Create element logic in multiple Renderers -> Unify using modules/ui/elements.js or utility functions.

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Common Refactoring Techniques

Composing Methods

• Extract Method: Select a code segment -> Create new function -> Name it -> Replace original with function call.
• Inline Method: When the function body is clearer than its name, inline it back to the call site.
• Replace Temp with Query: Replace temporary variables with function calls to reduce local variable interference.

Organizing Data

• Encapsulate Field: (Less enforced in JS) Use getter/setter to encapsulate variable access.
• Replace Magic Number with Symbolic Constant: Replace 86400 with SECONDS_IN_DAY.

Simplifying Conditional Expressions

• Decompose Conditional: Extract complex if (a && b || c) into if (isSpecialCase()).
• Consolidate Conditional Expression: Merge conditional checks that have the same result.
• Replace Nested Conditional with Guard Clauses: Use Guard Clauses to return early, reducing nesting.

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Project-Specific Refactoring Guidelines (Arc-Like Chrome Extension)

1. Separate DOM Operations:

   • Avoid direct DOM manipulation in business logic (modules/stateManager.js).
   • Ensure all DOM generation is in *Renderer.js modules.
   • Ensure all DOM queries are in modules/ui/elements.js (if possible).

2. State Management:

   • Avoid relying on window.globalVar. Use stateManager module to hold cross-module state.

3. Chrome API Encapsulation:

   • Don't call chrome.bookmarks.* directly in UI components. Use modules/apiManager.js for future replacement or testing.

4. Style Consistency:

   • Avoid using element.style.color = 'red'. Use CSS classes (element.classList.add('error')) with index.css.

How to Use This Skill

When User requests "Refactor this file" or "Clean up this code":

1. Check: Read the file and compare against the Code Smells list above.
2. Plan: Propose a refactoring plan (e.g., "I will break this 100-line render function into 3 sub-functions").
3. Execute: Perform the modifications.
4. Verify: Ensure functionality remains consistent.