how to writing codes one time for diffrent situations?

how to writing codes one time for diffrent situations?

Hello, please look at this code that I wrote, I have to define screenWidth for two times and also I have to wrote my codes inside and outside window resize.
Is there a better way for this:

html
  1. <body>
        <div class="first">First</div>
        <div class="secound">Socound</div>
    </body>
jQuery
  1. $(document).ready(function(){
        var screenWidth = $(window).width();
            if(screenWidth <= 980){
                $('.first').insertAfter('.secound');
            }
       
       
        $(window).on('resize', function(){
            var screenWidth = $(window).width();
            if(screenWidth <= 980){
                $('.first').insertAfter('.secound');
            }else{
                $('.first').insertBefore('.secound');
            }
        })
    });

demo:
http://jsfiddle.net/sabeti05/z0kkuz70/

thank you