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JS Variables and Scopes

Getting Started with JavaScript

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Introduction to JavaScript

Section titled “Introduction to JavaScript”

Adding JavaScript to an HTML Document

Section titled “Adding JavaScript to an HTML Document”

You can add JavaScript in three ways: internal/embedded, external, and inline.

1. Inline JavaScript

Section titled “1. Inline JavaScript”

You can add JavaScript directly within an HTML element using the onclick, onmouseover, and other event attributes.

<button onclick="console.log('Hello, World!')"> Click Me </button>
html
  • The JavaScript statement(s) run when the event (e.g., onclick) is triggered.

2. Internal JavaScript

Section titled “2. Internal JavaScript”

You can also write JavaScript inside the <script> tags, usually placed in the <head> or just before the closing </body> tag. This is the most common approach for adding JavaScript directly to an HTML document.

Inside <head>:

Section titled “Inside <head>:”
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Internal JavaScript Example</title>
    <script>
        // This is the JavaScript code
        function showMessage() {
            alert('Hello from internal JavaScript!');
        }
    </script>
</head>
<body>
    <button onclick="showMessage()">Click me</button>
</body>
</html>
html

3. External JavaScript

Section titled “3. External JavaScript”
  • It’s common to place JavaScript in a separate file and link it to your HTML. This makes your code more organized and reusable.
  • This is the cleanest and most efficient method for adding JavaScript to a webpage, especially for larger projects.
Example: Linking an External JavaScript File
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>External JavaScript Example</title>
</head>
<body>
    <button onclick="showMessage()">Click me</button>


    <!-- Linking the external JavaScript file -->
    <script src="script.js" type="text/javascript"></script>
</body>
</html>
html
script.js
// script.js
function showMessage() {
    alert('Hello from external JavaScript!');
}
javascript

When to Use Each Method?

Section titled “When to Use Each Method?”
  • Inline JavaScript: Use for simple interactions tied to specific elements (small snippets).
  • Internal JavaScript: Ideal for small-to-medium projects or when you don’t want to manage multiple files.
  • External JavaScript: Best for larger projects for maintainability and separation of concerns.

Best Practices for Adding JavaScript

Section titled “Best Practices for Adding JavaScript”