I'm currently developing a website using asp.net core mvc for an assignment. The website features identity server for user authentication. I am attempting to display a pop-up alert once a user enters the correct login credentials and clicks the Login button (similar to a JavaScript alert). To achieve this, I have created a boolean property in the .cs file that is set to true when a user successfully logs in. In the .cshtml file, I have included a script block containing a function that triggers an alert when the boolean property is true. However, the problem I'm facing is that the function executes when the page is loaded (at which point the property is still false), even though I have configured it to fire only on button click. Any suggestions on what might be causing this issue?

Login.cshtml
@page
@model LoginModel

@{
    ViewData["Title"] = "Log in";
}

<div class="container w-50 text-center">
    <h1 class="display-4" style="margin-bottom: 80px;">@ViewData["Title"]</h1>
    <section>
        <form id="account" method="post">
            <h4>Use a local account to log in.</h4>
            <hr />
            <div asp-validation-summary="All" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Input.Email"></label>
                <input asp-for="Input.Email" class="form-control" />
                <span asp-validation-for="Input.Email" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Input.Password"></label>
                <input asp-for="Input.Password" class="form-control" />
                <span asp-validation-for="Input.Password" class="text-danger"></span>
            </div>
            <div class="form-group">
                <div class="checkbox">
                    <label asp-for="Input.RememberMe">
                        <input asp-for="Input.RememberMe" />
                        @Html.DisplayNameFor(m => m.Input.RememberMe)
                    </label>
                </div>
            </div>
            <div class="form-group">
                <button onclick="showAlert()" type="submit" class="btn btn-primary">Log in</button>
            </div>
            <div class="form-group">
                <p>
                    <a asp-page="./Register" asp-route-returnUrl="@Model.ReturnUrl">Register as a new user</a>
                </p>
            </div>
        </form>
    </section>
</div>
<script type="text/javascript">
    showAlert = function () {
        if (@LoginModel.alert) {
            alert("Logged in succesfully");
            @LoginModel.alert = false;
        }
    }
</script>

@section Scripts {
    <partial name="_ValidationScriptsPartial" />
}

Login.cshtml.cs
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text.Encodings.Web;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Authorization;
using BookingApp.ApplicationLogic.DataModel;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Identity.UI.Services;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.Extensions.Logging;

namespace BookingApp.Areas.Identity.Pages.Account
{
    [AllowAnonymous]
    public class LoginModel : PageModel
    {
        private readonly UserManager<User> _userManager;
        private readonly SignInManager<User> _signInManager;
        private readonly ILogger<LoginModel> _logger;
        [BindProperty] static public bool alert { get; set; } = false;

        public LoginModel(SignInManager<User> signInManager,
            ILogger<LoginModel> logger,
            UserManager<User> userManager)
        {
            _userManager = userManager;
            _signInManager = signInManager;
            _logger = logger;
        }

        [BindProperty]
        public InputModel Input { get; set; }

        public IList<AuthenticationScheme> ExternalLogins { get; set; }

        public string ReturnUrl { get; set; }

        [TempData]
        public string ErrorMessage { get; set; }

        public class InputModel
        {
            [Required]
            [EmailAddress]
            public string Email { get; set; }

            [Required]
            [DataType(DataType.Password)]
            public string Password { get; set; }

            [Display(Name = "Remember me?")]
            public bool RememberMe { get; set; }
        }

        public async Task OnGetAsync(string returnUrl = null)
        {
            if (!string.IsNullOrEmpty(ErrorMessage))
            {
                ModelState.AddModelError(string.Empty, ErrorMessage);
            }

            returnUrl = returnUrl ?? Url.Content("~/");

            // Clear the existing external cookie to ensure a clean login process
            await HttpContext.SignOutAsync(IdentityConstants.ExternalScheme);

            ExternalLogins = (await _signInManager.GetExternalAuthenticationSchemesAsync()).ToList();

            ReturnUrl = returnUrl;
        }

        public async Task<IActionResult> OnPostAsync(string returnUrl = null)
        {
            returnUrl = returnUrl ?? Url.Content("~/");

            if (ModelState.IsValid)
            {
                // This doesn't count login failures towards account lockout
                // To enable password failures to trigger account lockout, set lockoutOnFailure: true
                var result = await _signInManager.PasswordSignInAsync(Input.Email, Input.Password, Input.RememberMe, lockoutOnFailure: false);
                if (result.Succeeded)
                {
                    alert = true;
                    _logger.LogInformation("User logged in.");
                    return LocalRedirect(returnUrl);
                }
                if (result.RequiresTwoFactor)
                {
                    return RedirectToPage("./LoginWith2fa", new { ReturnUrl = returnUrl, RememberMe = Input.RememberMe });
                }
                if (result.IsLockedOut)
                {
                    _logger.LogWarning("User account locked out.");
                    return RedirectToPage("./Lockout");
                }
                else
                {
                    ModelState.AddModelError(string.Empty, "Invalid login attempt.");
                    return Page();
                }
            }

            // If we got this far, something failed, redisplay form
            return Page();
        }
    }
}