JavaScript makes HTML pages more dynamic and interactive.
Example
<html>
<body>
<h1>My First JavaScript</h1>
<button type="button"
onclick="document.getElementById('demo').innerHTML = Date()">
Click me to display Date and Time.</button>
<p id="demo"></p>
</body>
</html>
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
<html>
<body>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = "Hello JavaScript!";
</script>
</body>
</html> A Taste of JavaScript
Here are some examples of what JavaScript can do:JavaScript can change HTML content
<html>
<body>
<h1>My First JavaScript</h1>
<p>JavaScript can change the content of an HTML element:</p>
<button type="button" onclick="myFunction()">Click Me!</button>
<p id="demo">This is a demonstration.</p>
<script>
function myFunction() {
document.getElementById("demo").innerHTML = "Hello JavaScript!";
}
</script>
</body>
</html>
JavaScript can change HTML styles
<html>
<body>
<h1>My First JavaScript</h1>
<p id="demo">JavaScript can change the style of an HTML element.</p>
<script>
function myFunction() {
document.getElementById("demo").style.fontSize = "25px";
document.getElementById("demo").style.color = "red";
document.getElementById("demo").style.backgroundColor = "yellow";
}
</script>
<button type="button" onclick="myFunction()">Click Me!</button>
</body>
</html>JavaScript can change HTML attributes
<html>
<body>
<script>
function light(sw) {
var pic;
if (sw == 0) {
pic = "pic_bulboff.gif"
} else {
pic = "pic_bulbon.gif"
}
document.getElementById('myImage').src = pic;
}
</script>
<img id="myImage" src="pic_bulboff.gif" width="100" height="180">
<p>
<button type="button" onclick="light(1)">Light On</button>
<button type="button" onclick="light(0)">Light Off</button>
</p>
</body>
</html>
Try itThe 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
<html>
<body>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = "Hello JavaScript!";
</script>
<noscript>Sorry, your browser does not support JavaScript!</noscript>
<p>A browser without support for JavaScript will show the text written inside the noscript element.</p>
</body>
</html>HTML Script Tags
| Tag | Description |
|---|---|
| <script> | Defines a client-side script |
| <noscript> | Defines an alternate content for users that do not support client-side scripts |
