Auto Populate Current User Login Name in SharePoint

<script src="https://code.jquery.com/jquery-1.10.2.min.js" type="text/javascript"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery.SPServices/2014.02/jquery.SPServices-2014.02.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(document).ready(function() {
    // get the title of current user
    var UserName= $().SPServices.SPGetCurrentUser({
    fieldName: "Title",
    debug: false
});
//populate the field ‘Requestor’ with the current account
$('textarea[title="Requestor"]').val(UserName);
$('input[title="Requestor"]').val(UserName);
});
</script>

In following Image you can see current user name will be auto populated on page load.