JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <input class="test" type="text" />
</form>

JavaScript

function commaSeparateNumber(index, val) {
    val = val.replace(/\D/g, '');
    var array = val.split('');
    var index = -3;
    while (array.length + index > 0) {
        array.splice(index, 0, ',');
        // Decrement by 4 since we just added another unit to the array.
        index -= 4;
    }
    return array.join('');
};

$(document).on('keyup', '.test', function () {
    $(this).val(commaSeparateNumber);
});