JavascriptHow-ToBeginner · 3 min read

How to Comment in JavaScript: Syntax and Examples

In JavaScript, you can add comments using // for single-line comments and /* */ for multi-line comments. Comments are ignored by the browser and help explain your code.

📐

Syntax

JavaScript supports two types of comments:

Single-line comment: Starts with // and continues to the end of the line.
Multi-line comment: Starts with /* and ends with */, spanning multiple lines if needed.

javascript

// This is a single-line comment

/*
This is a multi-line comment
that spans multiple lines
*/

💻

Example

This example shows both single-line and multi-line comments in action. Comments do not affect the program output.

javascript

// Single-line comment
console.log('Hello, world!'); /* This prints a greeting */

Output

Hello, world!

⚠️

Common Pitfalls

Common mistakes include forgetting to close multi-line comments or trying to nest comments, which JavaScript does not support.

Also, placing code inside comments will prevent it from running.

javascript

/* This is a multi-line comment
console.log('This will not run'); // Missing closing */

// Wrong: Nested comments
/* Outer comment /* Inner comment */ Outer continues */

// Correct usage:
/* Outer comment
   Inner comment is not allowed, so just write plain text
*/

📊

Quick Reference

Comment Type	Syntax	Use Case
Single-line	// comment text	Short notes or explanations on one line
Multi-line	/* comment text */	Longer explanations or disabling blocks of code

✅

Key Takeaways

Use // for single-line comments and /* */ for multi-line comments in JavaScript.

Comments help explain code and are ignored when the program runs.

Never nest multi-line comments; JavaScript does not support this.

Always close multi-line comments properly to avoid syntax errors.