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Javascript Comments

Javascript Comments

JavaScript comments are used to elaborate JavaScript code that make it more readable. When testing alternative code, in order to prevent execution JavaScript comments are used.

There are 2 types of Comments we can define in JavaScript

  1. Single Line Comments
  2. Multi-line Comments

Single Line Comments

The Single line comments generally start with //.
A single-line comment is used here before each code line in this example:

Example 1 :

//this is single line comments
alert("Welcome Phptpoint");

Example 2 :

// Declare a, give it the value of 8
var a = 8; 

// Declare b, give it the value of x + 6     
var b = a + 6;  

Multi-line Comments

The Multi-line comments generally start with /* and end with */.
Any text written between /* and */ will be ignored by JavaScript.
A multi-line comment has been used in this example to explain the code:

Example

/*
The code below will change
the heading with id = "myH"
and the paragraph with id = "myP"
in my web page:
*/
document.getElementById("myH").innerHTML = "My World";
document.getElementById("myP").innerHTML = "My first World.";

Let's understand comments with another example:

A line will be treated as a comment if it begins with two forward slashes:
// Note to self: comments are good.

If you use this notation, you must put the slashes at the start of each comment line. This won’t work, for instance:

// Note to self:
comments are good.

Instead, you’d need to write

// Note to self:
// comments are good.

In order to comment out multiple lines like that, a forward slash can be placed and an Asterisk should be placed at the start of the comment block and an asterisk and forward slash at the end:

/* Note to self:
comments are good */