Get Login UserName fon Preload of SharePoint List "NewForm.aspx"

Step 1:  Downlaod SPServices.js latest files

Step 2: Place the J.s filed into Asset Libraries

Step 3 :Replace the url of the SP.Services to your Side from below yellow color highlighted url

Step 4: Change the first parameter Name which should be the column from "Title" to  your  list column name in the function
SetUserFieldValue("Title",loginName);

<script src="https://ajax.microsoft.com/ajax/jQuery/jquery-1.4.2.min.js" type="text/javascript"></script>

<script src="/SiteAssets/jquery.SPServices-2014.02.js" type="text/javascript"></script>


<script type="text/javascript">

$(document).ready(function () {

 var loginName= $().SPServices.SPGetCurrentUser();

SetUserFieldValue("Title",loginName);



function SetUserFieldValue(fieldName, userName) {

 var _PeoplePicker = $("div[title='" + fieldName + "']");

 var _PeoplePickerTopId = _PeoplePicker.attr('id');

 var _PeoplePickerEditer = $("input[title='" + fieldName + "']");

 _PeoplePickerEditer.val(userName);

 var _PeoplePickerOject = SPClientPeoplePicker.SPClientPeoplePickerDict[_PeoplePickerTopId];

 _PeoplePickerOject.AddUnresolvedUserFromEditor(true);

}

});
</script>