Comments help explain code (they are not executed and hence do not have any logic implementation). We can also use them to temporarily disable parts of your code.

1. Single Line Comments

A single-line comment in JavaScript is denoted by two forward slashes (//),

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

Hello Geeks!

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");  

Multiline comment in javascript

JavaScript Comments in HTML

Prerequisite : How to Add JavaScript in HTML Document?

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

<!DOCTYPE html>
<html>
<head>
    <title></title>
</head>
<body>
    <script>
        // Prinintg 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();

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Example 2: This example uses multi-line comments to prevent the 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();