（ document ）。ready（ function （）{

（ ＃btnRegister）。click（ function （）{
if （

（ #txtFirstname）。val（）== 0 ||

I've got problem: this script gets executed twice.

/// <reference path="jquery-1.8.2.min.js" />
$(document).ready(function () {

    $("#btnRegister").click(function () {
        if ($("#txtFirstname").val() == 0 || $("#txtNickname").val() == 0 || $("#txtGmail").val() == 0 || $("#txtPassword").val() == 0 || $("#txtBirth").val() == 0) {
            alert("Data Empty");
        }
        else {
            Register();
        }

    });


    function Register() {

        var IsMale = 1;
        var name = $("#txtFirstname").val();
        var nickName = $("#txtNickname").val();
        var email = $("#txtGmail").val();
        var password = $("#txtPassword").val();
        var birthDate = $("#txtBirth").val();
        alert(name);
        alert(nickName);
        alert(email);
        alert(password);
        alert(birthDate);
        alert(name);

        $.ajax({
            type: "GET",
            contentType: "application/json; charset=utf-8",
           
            url: "http://localhost:3148/api/values/5",

            success: function (data) {
                alert("Success 2");
                alert(data);
                var obj = jQuery.parseJSON(data);
                alert("ID =" + obj.longPachage.Id);
                window.location.href = "index.html";

            },
            error: function (data) {

                alert(" Error ");
            }
        })
    }

});

What I have tried:

i tried to execute without the button but still executed twice

(document).ready(function () {

("#btnRegister").click(function () { if (

("#txtFirstname").val() == 0 ||