JS Comment : Hiding Code



In order to make JavaScript more readable we should use as many as comments in Script. Comment is non executable Statement in the JavaScript.

Also See : Statements in JavaScript

Types of Comment in JavaScript

We can have two types of comment in JavaScript –

  1. Single Line Comment
  2. Multiple Line Comment

Single Line Comment in JavaScript

  1. Single Line comment starts with “//” symbol.
  2. Remaining line after “//” symbol is ignored by browser.
  3. End of Line is considered as End of the comment.

Example of Single Line Comment :

<script type="text/javascript">

// This is First Single Line Comment
document.write("<p>This is a paragraph 1</p>");

// Write two paragraphs
document.write("<p>This is a paragraph 2</p>");
document.write("<p>This is a paragraph 3</p>");

</script>

Multiple Line Comment in JavaScript

  1. Multi Line comment starts with “/*” symbol.
  2. Multi Line comment ends with “*/” symbol.
  3. Content written inside the multi-line comment is ignored by the browser.

Example of Multiple Line Comment :

<script type="text/javascript">
/* This is 
        Multiline 
              Comment */

document.write("<p>This is a paragraph 1</p>");
document.write("<p>This is a paragraph 2</p>");
document.write("<p>This is a paragraph 3</p>");
</script>

How to use Comment more efficiently in JavaScript

  1. Comment used for Documentation.
  2. Comment used to Hide Non-usable Code.
  3. Comment used to Hide Single Statement.
  4. Comment written after Statement

1. Comment used for Documentation

<script type="text/javascript">

/* This code is used to create function 
   which will call Google API for gmail.
   using this API we can view Gmail in PHP */

</script>

Above comment is used for documentation. We use This type of Documentation to summarize JS Code.

2. Comment used to Hide Non-usable line.

<script type="text/javascript">
// document.write("<h1>Heading</h1>");

document.write("<p>Google</p>");
document.write("<p>Yahoo</p>");
</script>

We have used comment to prevent execution of single line.

// document.write("<h1>Heading</h1>");

3. Comment used to Hide Non-usable Multiline Code.

/* document.write("<h1>Heading 1</h1>");
   document.write("<h1>Heading 2</h1>");
   document.write("<h1>Heading 3</h1>");
   document.write("<h1>Heading 4</h1>"); */

4. Comment written after Statement

<script type="text/javascript">
document.write("Hello "); // Write "Hello"
document.write("World");  // Write "World"
</script>