<!DOCTYPE html>
<html>
<head>
</head>
<body>
Enter a string: <input type="text" id="input-text-id" onselect="GetSelection()">
<script>
function GetSelection()
{
it = document.getElementById("input-text-id");
pid = document.getElementById("p-id");
pid.innerHTML = it.value.substring(it.selectionStart, it.selectionEnd);
}
/*
run:
I wrote "javascript" as text and select "cascri" that will show on "p-id"
*/
</script>
<p id="p-id"></p>
</body>
</html>