onclick event demo-4.html

<html>

<head>
	<script type="text/javascript">
		function display() {
			var name = document.getElementById("txt1").value;
			var sirnmae = document.getElementById("txt2").value;
			var fullname = name + " " + sirnmae;
			document.getElementById("txt1").value = name.toUpperCase();
			document.getElementById("txt2").value = sirnmae.toUpperCase();
			document.getElementById("disp").innerHTML = fullname.toUpperCase();
			document.getElementById("txt3").value = fullname.toUpperCase();
		}
	</script>
</head>

<body><br>

	<h3>Form demo</h3>

	Enter your name:<input type="text" id="txt1" /><br>
	Enter your sirname:<input type="text" id="txt2" /><br>
	Fullname:<input type="text" id="txt3" /><br>

	<button id="b1" onClick="display()">click me</button>
	<p id="disp"></p>

</body>

</html>