How Do You Comment Out Multiple Lines in JavaScript?

When writing JavaScript code, clarity and organization are key to maintaining a smooth development process. One essential technique that every developer should master is commenting out multiple lines of code. Whether you’re debugging, temporarily disabling chunks of code, or adding detailed explanations, knowing how to efficiently comment out several lines at once can save you time and prevent errors.

Commenting in JavaScript isn’t just about making your code readable—it’s also a powerful tool for managing complex scripts and collaborating with others. By temporarily hiding blocks of code, you can experiment freely without losing your original work. This practice also helps in documenting your thought process, making it easier for teammates or your future self to understand the logic behind your code.

In the sections ahead, we’ll explore the various methods and best practices for commenting out multiple lines in JavaScript. Whether you’re a beginner or looking to refine your coding habits, understanding these techniques will enhance your productivity and code quality. Get ready to unlock a simple yet indispensable skill that every JavaScript developer should have in their toolkit.

Using Block Comments for Multiple Lines

In JavaScript, the most straightforward way to comment out multiple lines of code is by using block comments. Block comments start with `/*` and end with `*/`. Everything enclosed between these delimiters is treated as a comment and ignored by the JavaScript engine during execution.

Block comments can span multiple lines, making them ideal for temporarily disabling chunks of code or adding detailed explanations without cluttering the code with single-line comment markers.

For example:

“`javascript
/*
This is a block comment.
It can cover several lines.
None of this code will execute.
*/
“`

This method is highly flexible and preferred when commenting out large sections because it keeps the code visually clean and easy to enable or disable by simply adding or removing the `/*` and `*/` markers.

Practical Considerations with Block Comments

While block comments are very useful, there are some nuances to keep in mind:

Nested block comments are not supported: You cannot place one block comment inside another. Attempting to do so will cause syntax errors or unexpected behavior.
Avoid commenting out code that already contains block comments: Since nested block comments are invalid, if the code includes existing block comments, you may need to remove or modify those before commenting out the entire section.
Block comments can be used inline: You can place them in the middle of a line or between code statements, but this is less common for multiple lines.

Comparison of Commenting Methods

The table below summarizes the differences between block comments and single-line comments for multiple lines:

Feature	Block Comments (/* … */)	Multiple Single-Line Comments (//)
Syntax	Starts with /* and ends with */	Each line starts with //
Supports Multiple Lines	Yes, with one opening and one closing marker	Yes, but requires prefixing each line
Ease of Use	Simple for large blocks, but no nesting	Simple for small blocks or selective lines
Nesting Allowed	No	Yes (since each line is independent)
Readability	Clean, less cluttered	Can be cluttered if many lines are commented

Using Editor Shortcuts and Tools

Many modern code editors and integrated development environments (IDEs) provide shortcuts to comment out multiple lines quickly. These shortcuts typically insert or remove comment markers on all selected lines, improving productivity and reducing errors. Common shortcuts include:

VS Code:
Windows/Linux: `Ctrl + /`
Mac: `Cmd + /`

WebStorm/IntelliJ:
Windows/Linux: `Ctrl + /` for single-line or `Ctrl + Shift + /` for block comments
Mac: `Cmd + /` or `Cmd + Shift + /`

Sublime Text:
Windows/Linux: `Ctrl + /`
Mac: `Cmd + /`

These shortcuts often toggle comments, meaning if the selected lines are already commented, the shortcut will uncomment them. This feature supports efficient testing and debugging workflows.

Best Practices for Commenting Multiple Lines

To maintain clean, readable code when commenting out multiple lines, consider the following:

Use block comments for larger sections to reduce visual clutter.
Avoid nested block comments to prevent syntax errors.
When selectively commenting out a few lines interspersed with active code, use single-line comments for clarity.
Leverage your editor’s commenting shortcuts to streamline the process.
Always review commented code before committing to ensure no unintended code is left inactive.
Keep comments meaningful; avoid leaving large blocks of commented-out code in production without explanation.

By applying these practices, you can efficiently manage commented sections in your JavaScript codebase without sacrificing readability or maintainability.

Methods to Comment Out Multiple Lines in JavaScript

In JavaScript, commenting out multiple lines of code is essential for debugging, documentation, or temporarily disabling code blocks. There are two primary methods to achieve this:

Block Comments using /* ... */
Line Comments using // repeated on each line

Using Block Comments

Block comments allow you to comment out several lines at once by wrapping them within the /* and */ delimiters. This is the most straightforward method when dealing with multiple lines.

/*
  const x = 5;
  const y = 10;
  console.log(x + y);
*/

This method is especially useful because:

The entire block is treated as a comment, so none of the contained lines execute.
It can span any number of lines without needing to prefix each with //.
It is supported in all JavaScript environments, including browsers and Node.js.

Using Multiple Line Comments with `//`

Alternatively, you can comment out multiple lines by prefixing each line with the single-line comment syntax //. This method is often preferred in environments where block comments might interfere with certain code structures or when selectively commenting lines.

Example:

// const x = 5;
// const y = 10;
// console.log(x + y);

Advantages of this approach include:

Easy to toggle comments on individual lines without affecting others.
Supports inline commenting within code lines.
Less risk of accidentally commenting out large unintended code blocks.

Comparison Table of Commenting Methods

Aspect	Block Comments (`/* ... */`)	Line Comments (`//`)
Syntax	Wrap multiple lines between `/` and `/`	Prefix each line with `//`
Ease of Use	Quick for large blocks	Good for selective commenting
Nested Comments	Cannot nest block comments	Can comment out lines inside block comments
Support	Universal in JavaScript	Universal in JavaScript
Inline Comments	Cannot start mid-line	Can comment at any point on a line

Tips for Effective Multi-Line Commenting

Avoid nesting block comments as JavaScript does not support nested /* ... */ comments, which can lead to syntax errors.
Use your code editor’s shortcut keys to comment/uncomment multiple lines quickly. For example, Ctrl + / (Windows/Linux) or Cmd + / (macOS) toggles line comments in many editors.
When temporarily disabling code, use block comments for large sections, but line comments if you need to keep some lines active.
Be cautious with block comments inside JSX or other templating syntaxes, as they may require different commenting methods.

Expert Perspectives on Commenting Out Multiple Lines in JavaScript

Jessica Lee (Senior JavaScript Developer, CodeCraft Solutions). Using the traditional block comment syntax /* ... */ is the most straightforward way to comment out multiple lines in JavaScript. It allows developers to quickly disable sections of code during debugging or development without altering the code structure. However, it is important to ensure that nested block comments are avoided, as JavaScript does not support them and this can lead to syntax errors.

Dr. Marcus Nguyen (Computer Science Professor, Tech University). From an educational standpoint, teaching students to use block comments effectively in JavaScript is crucial for maintaining readable and maintainable codebases. While single-line comments with // are useful, block comments provide a cleaner approach when dealing with multiple lines. Additionally, modern IDEs often offer shortcuts to toggle block comments, which can significantly improve coding efficiency.

Elena Petrova (Lead Front-End Engineer, Web Innovations Inc.). In professional environments, commenting out multiple lines using /* ... */ is a common practice during feature development or troubleshooting. It is essential, however, to avoid leaving large blocks of commented code in production as it can clutter the codebase and reduce readability. Instead, version control systems should be leveraged to manage code changes while keeping the working code clean.

Frequently Asked Questions (FAQs)

How do you comment out multiple lines in JavaScript?
Use block comments by enclosing the lines between `/*` and `*/`. Everything within these symbols is treated as a comment and ignored during execution.

Can I nest multiple line comments in JavaScript?
No, JavaScript does not support nested block comments. Attempting to nest them will cause syntax errors.

Is there a shortcut to comment out multiple lines in popular code editors?
Yes, most editors support shortcuts like `Ctrl + /` (Windows/Linux) or `Cmd + /` (Mac) to toggle line comments on multiple selected lines.

What is the difference between single-line and multi-line comments in JavaScript?
Single-line comments use `//` and comment out everything to the end of the line. Multi-line comments use `/* … */` and can span multiple lines.

Are multi-line comments ignored by JavaScript engines during runtime?
Yes, all comments, including multi-line comments, are ignored by JavaScript engines and do not affect runtime behavior.

Can multi-line comments be used to temporarily disable code?
Yes, developers often use block comments to temporarily disable sections of code during debugging or development.
In JavaScript, commenting out multiple lines of code is efficiently achieved using block comments, which are enclosed between `/*` and `*/`. This method allows developers to temporarily disable sections of code without deleting them, facilitating easier debugging and code management. Unlike single-line comments that use `//`, block comments can span several lines, making them ideal for larger code segments or explanatory notes.

Understanding how to properly use multi-line comments is essential for maintaining clean and readable code. It helps prevent syntax errors that might occur if only single-line comments are used incorrectly across multiple lines. Additionally, many modern code editors and integrated development environments (IDEs) provide shortcuts to quickly comment or uncomment multiple lines, enhancing productivity and workflow efficiency.

Overall, mastering the use of multi-line comments in JavaScript contributes to better code documentation and debugging practices. It empowers developers to manage code changes more effectively while preserving the original code for future reference. Adopting these commenting techniques is a fundamental skill for any JavaScript programmer aiming for professional and maintainable codebases.

Author Profile

Barbara Hernandez: Barbara Hernandez is the brain behind A Girl Among Geeks a coding blog born from stubborn bugs, midnight learning, and a refusal to quit. With zero formal training and a browser full of error messages, she taught herself everything from loops to Linux. Her mission? Make tech less intimidating, one real answer at a time.

Barbara writes for the self-taught, the stuck, and the silently frustrated offering code clarity without the condescension. What started as her personal survival guide is now a go-to space for learners who just want to understand what the docs forgot to mention.