JSFiddle - React, Tailwind, and code Playground

HTML

<input id="nev" list="nevek">
<datalist id="nevek">
   <option value="János" data-value="janos">
   <option value="Péter" data-value="peter">
   <option value="Pál" data-value="pal">
</datalist>

JavaScript

$("#nev").bind('input', function ()
{   
    var find_this = this.value.charAt(0).toUpperCase() + this.value.slice(1);
    var data_value = $('#nevek').find('option[value="' + find_this + '"]').attr('data-value');
    if (data_value)
        alert ( data_value );
});