Javascript function returns Undefined

Question

Hello !

I have a Javascript function where I use ajax , I need the return of this function to be the data that is returned by ajax. I can get the return smoothly but I can’t assign the return value to a variable to return to the function. The function is always returning Undefined, someone can help me ???

function verifica_cep_cliente(){

            var var_endereco_selecionado = $('#endereco_entrega_utilizar').val();
            var cliente_selecionado = '<?php echo $this->session->cliente_externo_logado ?>';
            var var_forma_entrega = '<?php echo $this->session->FORMAENTREGA_CODIGO ?>';
            var retorno;

            $.ajax({
               url: '<?php echo base_url('Pagamento/verifica_cep_cliente_ajax') ?>',
               type: 'POST',
               dataType: 'TEXT',
               data:"endereco_entrega="+var_endereco_selecionado +"&cliente="+ cliente_selecionado+"&formaentrega="+var_forma_entrega,
               success: function (result){
                   //return result; 
                   retorno = result;
               }
            }); 

           //return retorno;


           alert("retorno " . retorno);


        }