JavaScript Tutorial
Comments in JavaScript are non-executable lines used to explain, document, or temporarily disable code. They are ignored by the JavaScript engine but are essential for readability, maintainability, and collaboration.
Why this matters
Whether you build small scripts or large applications in React/Next.js, effective comments are a professional habit that improves team velocity and code clarity.
A comment is text in code that the engine ignores during execution.
JavaScript supports three main comment styles:
Single-line comments begin with // and apply to the rest of that line.
Multi-line comments span across lines and are useful for longer descriptions.
JSDoc comments provide structured metadata for functions/classes and improve tooling support in editors.
Avoid commenting obvious lines that are already clear from good naming and structure.
Prefer expressive code first, then comments where necessary.
Comments do not affect execution, but they improve readability, debugging, collaboration, and documentation quality.
Three key styles: single-line (//), multi-line (/* */), and JSDoc (/** */).
Mature developers prioritize clear code and add comments where they bring real value.
// This is a single-line comment
console.log("Hello World"); // Prints greeting message
let total = 100; // Initial total amountEverything after // on the same line is ignored by JavaScript.
/*
This is a multi-line comment.
It can span multiple lines.
*/
console.log("Learning JavaScript");
/*
Calculate final price
after applying discount and tax
*/
let finalPrice = price - discount + tax;Use this format for longer explanations or temporary block-level disabling.
/**
* Adds two numbers
* @param {number} a
* @param {number} b
* @returns {number}
*/
function add(a, b) {
return a + b;
}JSDoc improves editor hints and documentation quality in professional projects.
"use strict";
/**
* Calculates discount based on user type
* @param {string} userType
* @param {number} price
* @returns {number}
*/
function calculateDiscount(userType, price) {
// Premium users get 20% discount
if (userType === "premium") {
return price * 0.8;
}
// Regular users get 10% discount
return price * 0.9;
}Demonstrates strict mode, JSDoc, and meaningful logic comments together.
Prefer expressive naming and clean structure; comment only where extra context is needed.
Update comments during refactors to avoid misleading documentation.
Always close /* ... */ properly to avoid syntax errors.
No. Comments are ignored by the engine and do not execute.
No. Comment intent and complex logic, not obvious statements.
Use JSDoc for shared modules, utility functions, and larger codebases where API clarity matters.
Yes. Temporarily disabling lines and adding context comments can speed up debugging.