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JavaScript in Practice: Getting Started

How to Write Comments in JavaScript?

Understand the purpose of comments in JavaScript and learn how to write both single-line and multi-line comments. This lesson helps you write clearer, more readable code by using appropriate commenting techniques, similar to styles used in languages like C++ and Java.

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We often place comments in our code so that we know what it is doing.

JavaScript is similar to C++ and Java in its commenting style:

  • Everything between /* and */ is ignored by the interpreter.
  • Everything after // on the same line is ignored by the interpreter.
Node.js
 
let a = 5 + 2; // This is a single line comment lasting until the end of the line.
 
/*
     A comment that can span multiple lines.
     Everything inside the comment will be ignored by the JavaScript interpreter.
     let b = 2;
*/

The above two comments are interpreted as:

Node.js
let a = 5 + 2;

Everything else is ignored.

Why do we use comments? To avoid ending up in similar situations:

Node.js
// Dear maintainer:
// 
// Once you are done trying to 'optimize' this routine,
// and have realized what a terrible mistake that was,
// please increment the following counter as a warning
// to the next guy:
// 
// total_hours_wasted_here = 42
//

My other favorite is:

Node.js
// I dedicate all this code, all my work, to my wife, Darlene, who will 
// have to support me and our three children and the dog once it gets 
// released into the public.

Try to write readable code with good comments.