Get the value of a textbox using javascript sample code:
<!DOCTYPE html>
<html>
<head>
<script>
// access the value of the above textbox
var name = document.getElementById('txtFriendName').value;
alert(name);
</script>
<head>
<body>
Friend name: <input type="text" id="txtFriendName" name="FirstName" value="Dhruv Sheth">
</body>
</html>