JavaScript Comments

Comments are used to explain your code and make it easier to understand. They are ignored by JavaScript and do not affect how the code runs.

1. Single Line Comments

A single-line comment in JavaScript starts with //. Anything after // on that line is ignored by JavaScript and does not get executed.

// A single line comment  
console.log("Hello Coders!");    

Output:

Hello Coders!

2. Multi-line Comments

A multiline comment begins with /* and ends with */

/* It is multi line comment.  
It will not be displayed upon 
execution of this code */  
 
console.log("Multiline comment in javascript");  

Output:

Multiline comment in javascript

JavaScript Comments in HTML

Prerequisite: How to Add JavaScript in HTML Document?

The syntax of comments remains the same when we write inside the HTML <script> tag.

<!DOCTYPE html>
<html>
<head>
    <title></title>
</head>
<body>
    <script>
        // Printing Hello World
        document.write('Hello World');
    </script>
</body>
</html>

JavaScript Comments to Prevent Execution

We can use // or /*…*/ to change the JavaScript code execution using comments. JavaScript Comments are used to prevent code execution and are considered suitable for testing the code.

function add() {
    let x = 10;
    let y = 20;
    let z = x + y;
    // console.log(x + y);
    console.log(z);
}
 
add();

Output:

30

Example 2: Multi-line comments to prevent execution of addition code and perform subtraction operations.

function sub() {
    let x = 10;
    let y = 20;
    /* let z = x + y;
    console.log(z); */
 
    let z = x - y;
    console.log(z);
}
 
sub();

Output:

-10