JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    radio 1
    <input type="radio" data-mymodaltabindex="1" />
    radio 2
    <input type="radio" data-mymodaltabindex="2" />
</div>
<div>
    text
    <input type="text" data-mymodaltabindex="3" />
</div>

CSS

.highlight {
    background-color:#FF6;
    border: 1px solid #FC6;
}

JavaScript

$('[data-mymodaltabindex]').blur(function () {        
   $(this).parent().removeClass('highlight');
   console.log('blur ' + $(this));
});

$('[data-mymodaltabindex]').focus(function () {
   $(this).parent().addClass('highlight');
   console.log('highlight ' + $(this));
});

function getModalClosestHighValue(a, x) {
    var hi;
    for (var i = a.length; i--; ) {
        if (a[i] > x && (hi === undefined || hi > a[i])) hi = a[i];
    };
    return hi;
}

function getModalClosestLowValue(a, x) {
    var lo;
    for (var i = a.length; i--; ) {
        if (a[i] < x && (lo === undefined || lo < a[i])) lo = a[i];
    };
    return lo;
}
$('[data-mymodaltabindex]').on('keydown', function (e) {
    if (e.keyCode == 9 || e.which == 9) {
        // define variables
        var mytabindex = null;
        var maximum = null;
        var minimum = null;
        var next = null;
        var previous = null;
        var values = new Array();
        // set mytabindex on the actual focused control
        var mytabindex = $(this).attr('data-mymodaltabindex');
        // put every visible mytabindex into array
        $('[data-mymodaltabindex]:visible').each(function () {
            values.push(parseInt($(this).attr('data-mymodaltabindex')));
        });
        //console.log(values);
        // look for maximum minimum mytabindex 
        // for maximum and minimum we filter out null values 
        // as they are interpreted as 0 with math functions
        maximum = Math.max.apply(null, values.filter(function (val) { return val !== null }));
        minimum = Math.min.apply(null, values.filter(function (val) { return val !== null }));
        // set next and previous using function
        next = getModalClosestHighValue(values, mytabindex);
        previous = getModalClosestLowValue(values, mytabindex);
        // go back to begining / end if 
        // end / begining is reached
        if (!previous) { previous = maximum; }
        if (!next) { next = minimum; }
       ...