JSFiddle - React, Tailwind, and code Playground

HTML

<button>1</button><button>2</button>

JavaScript

$('button').click(function() {
        var val = $(this).html();
        
        swap(val);
    });

    var boxArray = ["1","2","3","4","5","6","7","8","9","10","11","12","13","14","15",""]

    function swap(el) {
        var blankIndex = boxArray.indexOf(""),
            elIndex = boxArray.indexOf(el);
        
        boxArray[blankIndex] = el;
        boxArray[elIndex] = "";
        
        console.log(boxArray);
    }