JSFiddle - React, Tailwind, and code Playground

HTML

<fieldset class="fsResDir">
    <legend>Dados do Cartão&nbsp;</legend>
    <input type="radio" name="RadBand" id="visa" />
    <label for="visa">
        <img src="visa.png" />
    </label>
    <input type="radio" name="RadBand" id="mast" />
    <label for="mast">
        <img src="master.png" />
    </label>
    <input type="radio" name="RadBand" id="amex" />
    <label for="amex">
        <img src="amex.png" />
    </label>
    <label for="val" class="lab90">Validade:</label>
    <input type="text" class="ent20Form" id="val" name="TxtValMes" />/
    <input type="text" class="ent40Form" name="TxtValAno" />
    <label for="num" class="lab90">Numero:</label>
    <input type=text class="ent120Form" id="num" name="TxtNumero" />
    </div>
</fieldset>

JavaScript

var cartoes = {
    visa: /^4[0-9]{12}(?:[0-9]{3})/,
    mast: /^5[1-5][0-9]{14}/,
    amex: /^3[47][0-9]{13}/
};

document.getElementById('num').addEventListener('keyup', testarCC);
var inputs = document.querySelectorAll('.fsResDir input[type="radio"]');

function testarCC(e) {
    var nr = this.value;
    var tipo;
    for (var cartao in cartoes) if (nr.match(cartoes[cartao])) tipo = cartao;
    if (tipo) document.getElementById(tipo).click();
    else for (var i = 0; i < inputs.length; i++) inputs[i].checked = false;
}