JavaScript Comment

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The objective of the comments is identical in all programming language to improve the readability of the code. Comments play a major role to help a programmer in debugging. These comments are not compiled by browser, It helps the programmer while modification and maintenance to understand the code.

Usage of Comments:
a) It can used to deliver message, suggestions, and warning related to your code in a meaningful manner.
b) Increase code readability.
c) To make some code disable for the compiler
d) Simplify code maintenance

For Example
Suppose we have used 5 variables in our problem. A for addition, S for subtraction, M for multiplication, D for division, R for reminder. To make other programmers understand my code, I can use comment that I have used 5 variables for the code.

In JavaScript, Comments are also of two type's i.e. Single line and multi-line like other programming languages.

Single Line
Single line comments can be represented through double forward slashes (//). We can use it on both before as well as after statement depending upon the situation.

Let's demonstrate this concept through two examples:

Ist Program

<script>
// Single line comment
document.write("WELCOME STUDENTS");
</script>

2nd Program

<script>
var p=40; // Declare p
var q=20; // Declare q
var r=p-q; // It adds values of  p and q variable
document.write(r); // prints subtraction
</script>

Multi-line Comments
Multiline comments are used for providing small description about your code. These can be used with forward slash along with asterisk

Example

/* code description */

How one can change the content in JavaScript through getElementById()

Example

<!DOCTYPE html>
<html>
<body>
<h2> What is JavaScript ? </h2>
<p id="demo"> JavaScript is scripting language lets start tutorial </p>
<button
 type="button" 
onclick='document.getElementById("demo").innerHTML="welcome in 
javascript tutorial!"'> Click Me! </button>
</body>
</html>

JavaScript can modify HTML styles demonstrated in output

Output: