Using JavaScript in HTML

1. Inline JavaScript

Inline JavaScript is code written directly within HTML tags, often used for simple tasks like handling click events on buttons.

Here’s an example of inline JavaScript to display an alert when a button is clicked:

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<button onclick="alert('Hello, world!')">Click Me</button>
                    

In this example, the onclick attribute triggers a JavaScript alert() function when the button is clicked.

2. External JavaScript

External JavaScript keeps the JavaScript code separate from the HTML file, improving readability and maintainability. It’s ideal for larger scripts that you might use across multiple pages.

To use an external JavaScript file, link to it with the <script> tag in the HTML file:

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<!-- HTML File -->
<button onclick="displayMessage()">Click Me</button>
<script src="scripts/myScript.js"></script>
                    

Here’s the content of myScript.js:

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// myScript.js
function displayMessage() {
    alert("Hello from an external JavaScript file!");
}
                    

In this setup, clicking the button calls the displayMessage function from the external JavaScript file myScript.js.

3. Internal JavaScript in the <script> Tag

You can also add JavaScript inside your HTML file within a <script> tag, which is useful for scripts that don’t need to be reused on other pages.

Here’s an example:

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<button onclick="showGreeting()">Click for Greeting</button>
<script>
function showGreeting() {
    alert("Welcome to JavaScript in HTML!");
}
</script>
                    

In this example, the showGreeting function is written directly in the HTML file within a <script> tag.

4. Choosing Inline vs. External JavaScript

While inline JavaScript is suitable for small tasks, it’s best practice to use external files for larger scripts or when the same script is used on multiple pages. This keeps your HTML cleaner and makes your code more maintainable.

Using external files also improves page load time because browsers can cache these files, reducing the need to download them again on subsequent page loads.

5. Conclusion

JavaScript can be added to HTML in various ways depending on the project’s needs. Understanding when to use inline, internal, or external JavaScript will help you keep your code organized and optimized.