JavaScript Introduction
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JavaScript Can Change HTML Content
One of many HTML methods is getElementById().
This example uses the method to “find” an HTML element (with id=”demo”), and changes the element content (innerHTML) to “Hello JavaScript”:
<!DOCTYPE html>
<html>
<body>
<h1>What Can JavaScript Do?</h1>
<p id="demo">JavaScript can change HTML content.</p>
<button type="button"
onclick="document.getElementById('demo').innerHTML = 'Hello JavaScript!'">
Click Me!</button>
</body>
</html>
Save file name like : html_js1.html
JavaScript Can Change HTML Attributes
This example changes an HTML image, by changing the src attribute of an <img> tag:
<!DOCTYPE html>
<html>
<body>
<h1>JavaScript Can Change Images</h1>
<img id="myImage" onclick="changeImage()" src="pic_bulboff.gif" width="100" height="180">
<p>Click the light bulb to turn on/off the light.</p>
<script>
function changeImage() {
var image = document.getElementById('myImage');
if (image.src.match("bulbon")) {
image.src = "pic_bulboff.gif";
} else {
image.src = "pic_bulbon.gif";
}
}
</script>
</body>
</html>
Attached Image(Download): Image1 Image2
Save file name like : html_js2.html
JavaScript Can Change HTML Styles (CSS)
Changing the style of an HTML element, is a variant of changing an HTML attribute:
<!DOCTYPE html>
<html>
<body>
<h1>What Can JavaScript Do?</h1>
<p id="demo">JavaScript can change the style of an HTML element.</p>
<script>
function myFunction() {
var x = document.getElementById("demo");
x.style.fontSize = "25px";
x.style.color = "red";
}
</script>
<button type="button" onclick="myFunction()">Click Me!</button>
</body>
</html>
Save file name like : html_js3.html
JavaScript Can Validate Data
JavaScript is often used to validate input:
<!DOCTYPE html>
<html>
<body>
<h1>JavaScript Can Validate Input</h1>
<p>Please input a number between 1 and 10:</p>
<input id="numb">
<button type="button" onclick="myFunction()">Submit</button>
<p id="demo"></p>
<script>
function myFunction() {
var x, text;
// Get the value of the input field with id="numb"
x = document.getElementById("numb").value;
// If x is Not a Number or less than one or greater than 10
if (isNaN(x) || x < 1 || x > 10) {
text = "Input not valid";
} else {
text = "Input OK";
}
document.getElementById("demo").innerHTML = text;
}
</script>
</body>
</html>
Save file name like : html_js4.html
Source : w3schools.com