Change and disable field after selection

Question

I believe I already have a question answered more or less with what I want, but I do not know much of js and could not filter necessary information in what I read ... THEN!

I wonder how you could make it so that once I selected the <option value="Jurídica"> of my <select>, the <input id="name"> automatically change your placeholder="* Nome Completo" for placeholder="*Nome de sua Empresa" and that in the <input name="cpf"> were added to the property disabled or readonly.

<form>
    <select name="pessoa" id="pessoa">
        <option value="Não especificado">*Tipo de Pessoa</option>
        <option value="Física">Física</option>
        <option value="Jurídica">Jurídica</option>
    </select>

    <input name="nome" id="nome" placeholder="Nome Completo">
    <input name="icpf" id="icpf" placeholder="CPF">
    <input name="icnpj" id="icnpj" placeholder="CNPJ">

Follows form in Jsfiddle http://jsfiddle.net/LhanL/

Answer 1

You can do it like this: http://jsfiddle.net/z2jfx/

// select
var select = document.getElementById("pessoa");
// input
var input = document.getElementById("nome");

// quando o select muda
select.onchange = function () {
    var valor = select.options[select.selectedIndex].value;
    input.value = valor == 'Jurídica' ? '* Nome de sua Empresa' : '* Nome Completo';
}

This causes when the select changes, it will check whether the chosen value is 'Jurídica'. If the input changes to '* Nome de sua Empresa', otherwise '* Nome Completo'.

Note that these features can/should be done by a library like Mootools or jQuery that takes into account all the different ways browsers (especially old ones) react.

The code above is pure javascript and this is always faster (without loading library), I have now tested on IE7 and IE8.

To disable the input can use so in fa function onchange:

var habilitar = valor == 'Jurídica' ? true : false;
document.getElementById("icpf").disabled = habilitar;
document.getElementById("icnpj").disabled = !habilitar;

_{But I’m starting to find the solution too personalized.}