I do i know, when the JavaScript starts and ends? I fine it difficult to understand. Also how many codes(Sytax, Statements) can be written on one page?
Here’s a comprehensive list of commenting styles used in different programming languages:
Single-Line Comments
| Language | Syntax | Example |
|---|---|---|
| JavaScript | // | // This is a comment |
| Python | # | # This is a comment |
| Ruby | # | # This is a comment |
| PHP | // or # | // Comment or # Comment |
| SQL | -- | -- This is a comment |
| Bash/Shell | # | # This is a comment |
| C/C++/C# | // | // This is a comment |
| Java | // | // This is a comment |
| Swift | // | // This is a comment |
| Kotlin | // | // This is a comment |
| Go | // | // This is a comment |
| Rust | // | // This is a comment |
| MATLAB | % | % This is a comment |
| R | # | # This is a comment |
| Perl | # | # This is a comment |
| Haskell | -- | -- This is a comment |
| Lua | -- | -- This is a comment |
| PowerShell | # | # This is a comment |
| Assembly | ; or // | ;This is a comment |
| YAML | # | # This is a comment |
| F# | // | // This is a comment |
| Crystal | # | # This is a comment |
| Dart | // | // This is a comment |
| Groovy | // | // This is a comment |
| Scala | // | // This is a comment |
| Julia | # | # This is a comment |
Multi-Line Comments
| Language | Syntax | Example |
|---|---|---|
| JavaScript/Java/C/C++/C#/PHP | /* */ | /* This is a multi-line comment */ |
| Python | Triple quotes: ''' or """ | ''' Multi-line comment ''' or """ Multi-line comment """ |
| HTML | <!-- --> | <!-- This is a comment --> |
| CSS | /* */ | /* This is a comment */ |
| Swift | /* */ | /* This is a multi-line comment */ |
| Ruby | =begin and =end | =begin <br> Multi-line comment <br> =end |
| PowerShell | <# #> | <# This is a multi-line comment #> |
| SQL | /* */ | /* This is a comment */ |
| Kotlin | /* */ | /* This is a multi-line comment */ |
| Haskell | {- -} | {- This is a multi-line comment -} |
| Rust | /* */ | /* This is a multi-line comment */ |
| Go | /* */ | /* This is a multi-line comment */ |
| Lua | --[[ and ]] | --[[ Multi-line comment ]] |
| F# | (* *) | (* This is a multi-line comment *) |
| MATLAB | %{ and %} | %{ Multi-line comment %} |
| XML | <!-- --> | <!-- This is a comment --> |
| Dart | /* */ | /* This is a multi-line comment */ |
| Scala | /* */ | /* This is a multi-line comment */ |
Documentation Comments
| Language | Syntax | Example |
|---|---|---|
| Java | /** */ | /** Javadoc comment */ |
| JavaScript | /** */ | /** JSDoc comment */ |
| C# | /// | /// XML Documentation comment |
| Python | Docstrings: """ | """Docstring for documentation""" |
| Ruby | ## | ## RDoc comment |
| PHP | /** | /** PHPDoc comment */ |
| Rust | /// or //! | /// Doc comment for following item <br> //! Doc comment for enclosing item |
| Go | // | // GoDoc comment (before declaration) |
| Kotlin | /** | /** KDoc comment */ |
| Swift | /// | /// Swift documentation comment |
| Scala | /** | /** Scaladoc comment */ |
Would you like me to expand on any particular commenting style or how they’re used in practice?
Here are some examples of HTML pages with JavaScript in different locations. These examples will help you better understand where JavaScript begins and ends within a webpage.
Example 1: Inline JavaScript in HTML
<!DOCTYPE html>
<html>
<head>
<title>Inline JavaScript Example</title>
<!-- JavaScript in the head section -->
<script>
// JavaScript starts here
function greetUser() {
alert("Hello from the head section!");
}
// JavaScript ends here
</script>
</head>
<body>
<h1>My Web Page</h1>
<p>This page demonstrates different ways JavaScript appears in HTML.</p>
<button onclick="greetUser()">Greet from Head</button>
<!-- JavaScript in the body section -->
<script>
// Another JavaScript block starts here
function showMessage() {
document.getElementById('message').textContent = "Button was clicked at " + new Date().toLocaleTimeString();
}
// JavaScript ends here
</script>
<button onclick="showMessage()">Show Time</button>
<p id="message"></p>
<!-- Inline event handler (JavaScript is inside the HTML attribute) -->
<button onclick="alert('This is inline JavaScript directly in an HTML attribute!')">Click Me</button>
</body>
</html>
Example 2: External JavaScript File
<!DOCTYPE html>
<html>
<head>
<title>External JavaScript Example</title>
<!-- Link to external JavaScript file -->
<script src="script.js"></script>
</head>
<body>
<h1>External JavaScript Example</h1>
<p>The JavaScript for this page is stored in an external file called 'script.js'</p>
<button onclick="externalFunction()">Run External Function</button>
<p id="result"></p>
</body>
</html>
And here’s what might be in the external file named script.js:
// This entire file is JavaScript
function externalFunction() {
document.getElementById('result').textContent = "This function was called from an external file!";
}
// We can define variables
let counter = 0;
// And more complex functionality
function incrementCounter() {
counter++;
console.log("Counter is now:", counter);
}
Example 3: Multiple JavaScript Sections and Event Listeners
<!DOCTYPE html>
<html>
<head>
<title>Advanced JavaScript Example</title>
<style>
/* This is CSS, not JavaScript */
.highlight { background-color: yellow; }
</style>
</head>
<body>
<h1>Advanced JavaScript Integration</h1>
<div id="container">
<button id="btn1">Button 1</button>
<button id="btn2">Button 2</button>
<p id="display">Click a button</p>
</div>
<!-- First JavaScript block -->
<script>
// JavaScript starts here
// This code runs when the page loads
document.getElementById('display').textContent = "Page loaded at " + new Date().toLocaleTimeString();
// Variables defined in one script block are available to later script blocks
const appName = "My Demo App";
// JavaScript ends here
</script>
<!-- Second JavaScript block -->
<script>
// Another JavaScript block begins
// We can access variables from previous blocks
console.log("Running " + appName);
// Event listeners are another way to use JavaScript
document.getElementById('btn1').addEventListener('click', function() {
document.getElementById('display').textContent = "Button 1 was clicked";
document.getElementById('display').className = "highlight";
});
// JavaScript ends here
</script>
<!-- Third JavaScript block -->
<script>
// Yet another JavaScript block
document.getElementById('btn2').addEventListener('click', function() {
document.getElementById('display').textContent = "Button 2 was clicked";
document.getElementById('display').className = "";
});
// JavaScript ends here
</script>
</body>
</html>
These examples show different ways JavaScript can be incorporated into HTML pages. The key points to remember:
- JavaScript begins and ends with
<script>and</script>tags - You can have multiple script sections in a single HTML page
- You can place JavaScript in the
<head>or<body>sections - External JavaScript files keep your HTML cleaner
- Inline event handlers (like
onclick="...") contain JavaScript directly in HTML attributes - Event listeners are a cleaner alternative to inline handlers and are defined within script tags
Is there any specific part of these examples you’d like me to explain in more detail?