How to Add Comments in JavaScript

Comments in JavaScript are essential for making your code more understandable and maintainable. They allow you to explain what your code does, why certain decisions were made, or to temporarily disable parts of your code without deleting it. In this article, we'll explore how to add comments in JavaScript.

1. Single-Line Comments

Single-line comments in JavaScript start with two forward slashes //. Everything following the slashes on that line is treated as a comment and ignored by the JavaScript engine.


// This is a single-line comment
let x = 10; // This comment is at the end of a line

In this example, // This is a single-line comment is a comment that explains the code but does not affect its execution. Similarly, // This comment is at the end of a line is a comment that explains the variable x.

2. Multi-Line Comments

Multi-line comments are used for longer explanations or to comment out blocks of code. They start with /* and end with */. Anything between these symbols is treated as a comment.


/* This is a multi-line comment
   It can span multiple lines
   and is often used for longer explanations. */
let y = 20;

/* You can also use multi-line comments
   to temporarily disable code. */
// let z = 30; // This line of code is commented out

In this example, the multi-line comment explains the code and can span multiple lines. Additionally, multi-line comments can be used to comment out blocks of code that you may want to disable temporarily.

3. Commenting Out Code

Comments are also useful for disabling parts of your code. This is particularly handy during debugging or when testing different parts of your code.


// let a = 5;
let b = 10;

/* 
let c = 15;
let d = 20;
*/

In this example, the line // let a = 5; is a single-line comment that disables the code. The block /* let c = 15; let d = 20; */ is a multi-line comment that disables multiple lines of code.

4. Best Practices for Comments

While comments are useful, they should be used judiciously. Here are some best practices:

Keep comments concise: Comments should be short and to the point.
Avoid obvious comments: Don’t state the obvious. For example, avoid comments like // Increment x by 1 if the code is simply x++;.
Update comments as code changes: Ensure that your comments reflect the current state of your code.
Use comments to explain why: Explain the reasoning behind complex logic or decisions, rather than just describing what the code does.

5. Conclusion

Comments are a crucial part of writing readable and maintainable JavaScript code. Whether you're using single-line comments for brief explanations or multi-line comments for more detailed notes, it's important to use them effectively. Remember to keep your comments concise, relevant, and updated to ensure they add value to your code.

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