JS Comments

JavaScript Comments

JavaScript comments are used to explain the purpose of your code and make it more readable. Comments are not executed as a part of the program; they are solely meant for human developers to understand the code better. The browser simply ignores them.

You can use comments for various purposes, such as:

• Explaining the purpose of a particular piece of code.
• Adding documentation to your code for yourself and other collaborators.
• Temporarily disabling or "commenting out" a block of code for testing or debugging without permanently deleting it.

Tip: A good developer always writes clear comments to explain the why behind complex code logic.

Types of Comments in JavaScript

There are two common ways to write comments in JavaScript:

1. Single-line comments
2. Multi-line comments

1. Single-Line Comments in JavaScript

You can start a single-line comment with a double forward slash (//). Everything written after the // until the end of that specific line is treated as a comment.

Syntax:

// Defining the first string
var string1 = "JavaScript";

// Defining the second string
var string2 = "TypeScript";
// Printing the combined strings
document.write(string1, " and ", string2);

2. Multi-Line Comments in JavaScript

The multi-line comment is extremely useful when you need to comment out multiple lines of code or write a longer, detailed explanation. You can write multi-line comments between the /* and */ symbols.

Syntax:

let result = addition(100, 200);
document.write("Result = " + result);  

/* This function accepts two values as parameters,
   adds them together, and returns the computed result */
function addition(a, b) {
  return a + b;
}

3. Using Comments to Prevent Execution

In addition to providing information about the code, comments are frequently used during the debugging process to prevent the execution of a particular piece of code.

By commenting out a line or a block of code, you can test how your program runs without it, saving you the hassle of deleting and re-typing it later.

var bool1 = true;
var a = 100;
var b = 200;

// The line below is commented out, so bool1 remains true
// bool1 = false;
/* The block below is completely ignored by the browser:
a = a + b;
b = a - b;
a = a - b; 
*/
document.write("bool1 is: " + bool1 + "<br>"); // We can place a comment at the end of a line
document.write("a = " + a + ", b = " + b);