How to get the current logged in username in SharePoint 2013

Steps

1. Create page in your sharepoint site.
2. Edit the page and add a content editor webpart in sharepoint your page.
3. Copy hte below scitp in notepad and save it as a .js file in your site asset.
4. copy hte path of your notepad and paste it in a CEWP edit webpart link.
5. save the page .
6. out put will be displayed in alert box.

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>
<script type="text/javascript">
    var thisUserAccount ;
    $(document).ready(function() {
    thisUserAccount= $().SPServices.SPGetCurrentUser({
    fieldName: "Title",
    debug: false
});

alert(thisUserAccount);
});
</script>

Thanks for learning.