Change button value without showing alert

Question

I want to change the value of the button always with -1, without showing alert.

Follows code:

<button  onclick="alert(this.value);this.value -= 1;" value="200">200</button>

Answer 1

To prevent the alert from appearing, simply remove the call from alert().

Already to update the text button (which is not the same as the attribute value), you should also update the property innerHTML:

function diminuiValor(botao) {
    // diminui o "value"
    botao.value -= 1;
    // atualiza o texto do botão para ser o mesmo que o value
    botao.innerHTML = botao.value;
}

<button onclick="diminuiValor(this);" value="200">200</button>

Or, more directly (without creating a function):

<button onclick="this.value -= 1; this.innerHTML = this.value;" value="200">200</button>

In short, this.value -= 1 decreases the value that was set in the attribute value="200", as long as the innerHTML updates the button text. In the examples above I’m assuming you want to change both (because that’s what makes most sense to me).

Answer 2

See the example you want:

$("#id_do_botao").click(function() {
  var valor = this.value -= 1;
  $(this).text(valor);
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button id="id_do_botao" value="200">200</button>