What is the alternative to Ajax.BeginForms in Asp.net MVC core

You can use inline data-ajax-* attributes :

<form method="get"
      data-ajax-="true"
      data-ajax-method="get"
      data-ajax-url="/test">
      ...
</form>

• data-ajax
• data-ajax-url
• data-ajax-method
• data-ajax-mode
• data-ajax-update
• data-ajax-loading
• data-ajax-loading-duration
• data-ajax-confirm
• data-ajax-begin
• data-ajax-complete
• data-ajax-failure
• data-ajax-success

See Ajax Request Using Inline Attributes for some samples

Or you can call $.ajax from inside <scripts> tag:

$.ajax({
  url: "test.html",
  context: document.body
}).done(function() {
  $( this ).addClass( "done" );
});

See jQuery.ajax() for more details.

You can use https://github.com/mjebrahimi/AspNetCore.Unobtrusive.Ajax

1. Install nuget package called: AspNetCore.Unobtrusive.Ajax

2. In startup in ConfigureServices add the following line services.AddUnobtrusiveAjax(useCdn: true, injectScriptIfNeeded: false);

3. In razor page place @Html.RenderUnobtrusiveAjaxScript() at the end of body and after jquery Example of using instead of Ajax.BeginForm call:

   using (Html.AjaxBeginForm("SendComment",
   new AjaxOptions
   {
       HttpMethod = "Post",
       InsertionMode = InsertionMode.InsertAfter,
       UpdateTargetId = $"comments{Model.ExerciseId}",
       OnBegin = "ExerciseScripts.toggleLoading($(this), $(this));",
       OnSuccess = $"ExerciseScripts.toggleLoading($(this), $(this)); $('#textarea{Model.ExerciseId}').val('');",
       OnFailure = "Notice.showError();"
   }))
   {
       @Html.AntiForgeryToken()
       @Html.Hidden("exerciseId", Model.ExerciseId)
       @Html.TextArea("Comment", "",
           new {
               id = $"textarea{Model.ExerciseId}",
               @class = "form-control",
               placeholder = "Write you comment",
               required ="required"
           })
       <br />
       <button type="submit" class="btn btn-primary">
           <i class="fa fa-paper-plane-o fa-lg"></i>
           <span>Send</span>
       </button>
   }