JavaScript Comments

Comments are lines in a program that are ignored by JavaScript. They are used to explain code, improve readability, and make programs easier to understand.

Comments are extremely useful when working on large projects because they help developers understand the purpose of the code.

Why Use Comments?

Comments make programs cleaner and easier to maintain.

Types of JavaScript Comments

JavaScript supports two types of comments:

Single Line Comments

Single line comments are used to write comments on one line. They start with double forward slashes //.

// This is a single line comment

console.log("Hello JavaScript");

Explanation

Output

Hello JavaScript

Multiple Single Line Comments

// Program starts here

// Declaring variables

let name = "Ali";

// Printing output

console.log(name);

Multi Line Comments

Multi line comments are used when comments span across multiple lines. They start with /* and end with */.

/*

This is a
multi-line comment

*/

console.log("Welcome");

Explanation

Using Comments to Explain Code

Comments are commonly used to explain complex logic.

// Store student marks

let marks = 90;

// Check if student passed

if(marks >= 40){

    console.log("Pass");

}

Using Comments for Debugging

Developers often comment out code while testing programs.

let a = 10;

let b = 20;

// console.log(a + b);

console.log(a * b);

The addition statement will not execute because it is commented out.

Good Comment Example

// Calculate total price after discount

let price = 1000;

let discount = 200;

let total = price - discount;

console.log(total);

Bad Comment Example

// Variable

let x = 10;

// Console

console.log(x);

Bad comments do not explain anything meaningful. Good comments should explain the purpose of the code.

Shortcut for Comments in VS Code

Most code editors provide keyboard shortcuts for comments.

Nested Comments

JavaScript does not support nested multi-line comments.

/*

Outer comment

/* Inner comment */

*/

The above code may produce errors because nested multi-line comments are not allowed.

Real Life Example

// Student Information System

let studentName = "Rahul";

let marks = 85;

// Display student details

console.log(studentName);

console.log(marks);

Output

Rahul

85

Best Practices for Writing Comments

Important Notes

Summary