HTML JavaScript

JavaScript makes HTML pages more dynamic and interactive.
Example
My First JavaScript
The HTML <script> Tag
The <script> tag is used to define a client-side script (JavaScript).
The <script> element either contains scripting statements, or it points to an external script file through the src attribute.
Common uses for JavaScript are image manipulation, form validation, and dynamic changes of content.
To select an HTML element, JavaScript very often use the document.getElementById(id) method.
This JavaScript example writes "Hello JavaScript!" into an HTML element with id="demo":
Example
<script>
document.getElementById("demo").innerHTML = "Hello JavaScript!";
</script>
Tip: You can learn much more about JavaScript in our JavaScript Tutorial.
A Taste of JavaScript
Here are some examples of what JavaScript can do:
JavaScript can change HTML content
document.getElementById("demo").innerHTML = "Hello JavaScript!"; 
JavaScript can change HTML styles
document.getElementById("demo").style.fontSize = "25px";
document.getElementById("demo").style.color = "red";
JavaScript can change HTML attributes
document.getElementById("image").src = "picture.gif"; 
The HTML <noscript> Tag
The <noscript> tag is used to provide an alternate content for users that have disabled scripts in their browser or have a browser that doesn't support client-side scripts:
Example
<script>
document.getElementById("demo").innerHTML = "Hello JavaScript!";
</script>

<noscript>Sorry, your browser does not support JavaScript!</noscript>