You are previewing Maintainable JavaScript.

Maintainable JavaScript

Cover of Maintainable JavaScript by Nicholas C. Zakas Published by O'Reilly Media, Inc.
  1. Maintainable JavaScript
  2. SPECIAL OFFER: Upgrade this ebook with O’Reilly
  3. Introduction
  4. Preface
    1. Conventions Used in This Book
    2. Using Code Examples
    3. Safari® Books Online
    4. How to Contact Us
  5. I. Style Guidelines
    1. 1. Basic Formatting
      1. Indentation Levels
      2. Statement Termination
      3. Line Length
      4. Line Breaking
      5. Blank Lines
      6. Naming
      7. Literal Values
    2. 2. Comments
      1. Single-Line Comments
      2. Multiline Comments
      3. Using Comments
      4. Documentation Comments
    3. 3. Statements and Expressions
      1. Brace Alignment
      2. Block Statement Spacing
      3. The switch Statement
      4. The with Statement
      5. The for Loop
      6. The for-in Loop
    4. 4. Variables, Functions, and Operators
      1. Variable Declarations
      2. Function Declarations
      3. Function Call Spacing
      4. Immediate Function Invocation
      5. Equality
      6. eval()
      7. Primitive Wrapper Types
  6. II. Programming Practices
    1. 5. Loose Coupling of UI Layers
      1. What Is Loose Coupling?
      2. Keep JavaScript Out of CSS
      3. Keep CSS Out of JavaScript
      4. Keep JavaScript Out of HTML
      5. Keep HTML Out of JavaScript
    2. 6. Avoid Globals
      1. The Problems with Globals
      2. Accidental Globals
      3. The One-Global Approach
      4. The Zero-Global Approach
    3. 7. Event Handling
      1. Classic Usage
      2. Rule #1: Separate Application Logic
      3. Rule #2: Don’t Pass the Event Object Around
    4. 8. Avoid Null Comparisons
      1. Detecting Primitive Values
      2. Detecting Reference Values
      3. Detecting Properties
    5. 9. Separate Configuration Data from Code
      1. What Is Configuration Data?
      2. Externalizing Configuration Data
      3. Storing Configuration Data
    6. 10. Throw Your Own Errors
      1. The Nature of Errors
      2. Throwing Errors in JavaScript
      3. Advantages of Throwing Errors
      4. When to Throw Errors
      5. The try-catch Statement
      6. Error Types
    7. 11. Don’t Modify Objects You Don’t Own
      1. What Do You Own?
      2. The Rules
      3. Better Approaches
      4. A Note on Polyfills
      5. Preventing Modification
    8. 12. Browser Detection
      1. User-Agent Detection
      2. Feature Detection
      3. Avoid Feature Inference
      4. Avoid Browser Inference
      5. What Should You Use?
  7. III. Automation
    1. 13. File and Directory Structure
      1. Best Practices
      2. Basic Layout
    2. 14. Ant
      1. Installation
      2. The Build File
      3. Running the Build
      4. Target Dependencies
      5. Properties
      6. Buildr
    3. 15. Validation
      1. Finding Files
      2. The Task
      3. Improving the Target
      4. Other Improvements
      5. Buildr Task
    4. 16. Concatenation and Baking
      1. The Task
      2. Line Endings
      3. Headers and Footers
      4. Baking Files
    5. 17. Minification and Compression
      1. Minification
      2. Compression
    6. 18. Documentation
      1. JSDoc Toolkit
      2. YUI Doc
    7. 19. Automated Testing
      1. YUI Test Selenium Driver
      2. Yeti
      3. PhantomJS
      4. JsTestDriver
    8. 20. Putting It Together
      1. Missing Pieces
      2. Planning the Build
      3. Using a CI System
  8. A. JavaScript Style Guide
    1. Indentation
    2. Line Length
    3. Primitive Literals
    4. Operator Spacing
    5. Parentheses Spacing
    6. Object Literals
    7. Comments
      1. Single-Line Comments
      2. Multiline Comments
      3. Comment Annotations
    8. Variable Declarations
    9. Function Declarations
    10. Naming
    11. Strict Mode
    12. Assignments
    13. Equality Operators
    14. Ternary Operator
    15. Statements
      1. Simple Statements
      2. return Statement
      3. Compound Statements
      4. if Statement
      5. for Statement
      6. while Statement
      7. do Statement
      8. switch Statement
      9. try Statement
    16. White Space
    17. Things to Avoid
  9. B. JavaScript Tools
    1. Build Tools
    2. Documentation Generators
    3. Linting Tools
    4. Minification Tools
    5. Testing Tools
  10. Index
  11. About the Author
  12. Colophon
  13. SPECIAL OFFER: Upgrade this ebook with O’Reilly
  14. Copyright
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Chapter 2. Comments

Comments are often the least popular part of coding. They’re dangerously close to documentation, which is the last thing any developer wants to spend time doing. However, comments are incredibly important for the overall maintainability of the code. Opening a file without any comments may seem like a fun adventure, but when there are deadlines to meet, this task turns into torture. Appropriately written comments help tell the story of code, allowing other developers to drop into a part of the story without needing to hear the beginning. Style guidelines don’t always cover commenting styles, but I consider them important enough to warrant their own section.

JavaScript supports two different types of comments: single-line and multiline.

Single-Line Comments

Single-line comments are created by using two slashes and end at the end of the line:

// Single-line comment

Many prefer to include a space after the two slashes to offset the comment text. There are three ways in which a single-line comment is used:

  • On its own line, explaining the line following the comment. The line should always be preceded by an empty line. The comment should be at the same indentation level as the following line.

  • As a trailing comment at the end of a line of code. There should be at least one indent level between the code and the comment. The comment should not go beyond the maximum line length. If it does, then move the comment above the line of code.

  • To comment out large portions of code (many ...

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