How do I validate a value without leaving the page?

Question

I’m developing a system with the discount part, so I wanted the user to enter the discount and after he finished validating whether or not and show the discount percentage.

$cupom = $this->input->post('cupom_desconto');
$desconto = $this->desconto_model->buscarDesconto($cupom, $atividade_codigo);

This is the way I am doing, but this way is sending the request to another page and I would like it to be done on the same page, example of Netshoes and others that we put the code and if it is valid appears on the same page the value of the discount, if you have, otherwise does not change anything.

Answer 1

A suggestion is to do by jQuery.

I made an example for you:

Fiddle

Basically:

$("#valorPorcentagem").change(function(e, j){
    var valorDigitado = this.value;
    var valorProduto = 300.00;

    if (valorDigitado == "") {
        alert("Sem desconto!")   
    } else {
        alert("O produto terá um desconto de: " + valorDigitado + "%. Valor final do produto: R$" + ( ((100-valorDigitado)/100) * valorProduto));  
    }
});