<!DOCTYPE html>
<html lang="en-US">
<body>
<input type="text" onselect="myFunction()" value="select some text">
<p id="point"></p>
<script>
var x = document.getElementById("point");
function myFunction() {
var myVal= document.getElementsByTagName("input")[0].value
var len = myVal.length;
var activeEl = document.activeElement;
var selStart = activeEl.selectionStart;
var selEnd = activeEl.selectionEnd;
var mySelect = getSelection().toString();
var myChange = mySelect.toUpperCase();
var myData = myVal.slice(0, selStart)+""+myChange+""+myVal.slice(selEnd, len);
x.innerHTML = myData;
}
</script> </body>
</html>