JavaScript Comments

Introduction

In this tutorial, you will learn how to comment in JavaScript code. JavaScript code that is ignored by the JavaScript engine when the code is executed.

In JavaScript, comments are used to explain code, improve readability, and make maintenance easier. They are ignored by the JavaScript engine, meaning they don’t affect how the program runs.

It is used to explain code, make notes, or temporarily disable certain parts of the code.

Comments are helpful for both the developer writing the code and others who might read or maintain the code in the future.

What are JavaScript Comments?

JavaScript comments are lines of text added to the code that are not executed by the browser or JavaScript engine. They are used to describe what the code is doing or to leave notes for developers.

Why are Comments Used in JavaScript?

Comments play an important role in development for several reasons.

1. Improve Readability

Comments help developers understand the purpose of code quickly.

2. Documentation

They act as inline documentation for functions, variables, and logic.

3. Debugging

You can temporarily disable code using comments.

4. Collaboration

When working in a team, comments help other developers understand your code.

5. Maintenance

Makes it easier to update or modify code in the future.

Types of JavaScript Comments

There are two types of comments

Single-Line Comments

It is used for a single line. It is used to add short notes or explanations on one line.

They start with // and extend to the end of the line.

Syntax:

// This is a single-line comment

Example:

// This is a single-line comment
let name = 'John'; // Variable name is assigned the value John

Multi-Line Comments

It is used for Multi-Line Comments. It is used for longer explanations or for commenting out multiple lines of code.

They start with /* and end with */

Syntax:

/*
This is a multi-line comment
It can span multiple lines
*/

Example:

/*
This is a multi-line comment.
It can span multiple lines.
It is useful for longer descriptions or temporarily disabling blocks of code.
*/
let x = 10;

Real Life Example of Comments

In this example, you will see a function to calculate a discount.

// Function to calculate discount
function calculateDiscount(price, discount) {
   // Ensure discount is valid
   if (discount > 0 && discount <= 100) {
       let finalPrice = price - (price * discount / 100);
       return finalPrice;
   } else {
       // Return original price if discount is invalid
       return price;
   }
}

console.log(calculateDiscount(1000, 10));

Common Mistakes in JavaScript Comments

You will see some common mistakes in JavaScript Comments

1. Outdated Comments

// adds two numbers
let result = a - b; // incorrect comment

2. Overusing Comments

Too many comments can reduce readability.

3. Nested Comments (Not Allowed)

/* outer comment
  /* inner comment */  // Error
*/

Advanced: JSDoc Comments

JSDoc is a standard for documenting JavaScript code.

Example:

/**
* Adds two numbers
* @param {number} a
* @param {number} b
* @returns {number}
*/
function add(a, b) {
   return a + b;
}

Benefits:

1. Better documentation
2. IDE support
3. Useful for large projects

JavaScript Comments vs Documentation

JavaScript Comments – Interview Questions

JavaScript Comments – Objective Questions (MCQs)

Conclusion

JavaScript comments are a simple yet powerful tool that improves code readability, maintainability, and collaboration. Whether you're a beginner or an experienced developer, using comments effectively can make your code easier to understand and debug.

With the help of Comments, you can write clean and professional JavaScript code that others can easily understand.