Comments

JavaScript · Reference cheat sheet

📋 Overview

Comments document intent for humans. Engines ignore them. JavaScript supports single-line // and multi-line /* */ comments. JSDoc-style blocks are a convention for documenting APIs.

🔧 Core concepts

Comments do not replace clear names and small functions.

💡 Examples

Single-line and inline:

// Convert Celsius to Fahrenheit
const c = 20;
const f = c * 9 / 5 + 32; // standard formula
console.log(f);

Multi-line:

/*
  Demo script: comments + console output.
  Safe to delete when you understand it.
*/
console.log("ok");

JSDoc-style:

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

console.log(add(2, 3));

Comment out an experiment:

// const legacy = oldApi();
const value = newApi();
console.log(value);

⚠️ Pitfalls

• Nested /* */ is not allowed — the first */ ends the comment.
• // inside a string is not a comment: "http://example.com" is fine.
• Huge blocks of commented-out code belong in Git history, not the file.
• Misleading comments are worse than none — update them when code changes.

🔗 Related

• getting_started.md
• hello_world.md
• variables_let_const.md
• typeof_basics.md