Ajax works the same way, but instead of the @Ajax helper's, use the new MVC 6 Tag Helpers (don't forget to reference 'jquery' and 'jquery.unobtrusive-ajax' scripts).

JQuery Unobtrusive Ajax exists in the Asp.Net GitHub repo and can be Bower pulled.

Using the new MVC TagHelpers, you simply declare the form like the following:

<form asp-controller="Home" asp-action="SaveForm" data-ajax="true" data-ajax-method="POST">
...
</form>

To use the AjaxOptions that existed on the Ajax Helper on previous MVC versions, just add those attributes do the form tag like this:

<form asp-controller="Home" asp-action="SaveForm" data-ajax="true" data-ajax-method="POST" data-ajax-mode="replace" data-ajax-update="#content">
...
</form>
<div id="content"></div>

The HTML attributes (formerly AjaxOptions) that you can use in the form are the following (original source):

+------------------------+-----------------------------+
|      AjaxOptions       |       HTML attribute        |
+------------------------+-----------------------------+
| Confirm                | data-ajax-confirm           |
| HttpMethod             | data-ajax-method            |
| InsertionMode          | data-ajax-mode              |
| LoadingElementDuration | data-ajax-loading-duration  |
| LoadingElementId       | data-ajax-loading           |
| OnBegin                | data-ajax-begin             |
| OnComplete             | data-ajax-complete          |
| OnFailure              | data-ajax-failure           |
| OnSuccess              | data-ajax-success           |
| UpdateTargetId         | data-ajax-update            |
| Url                    | data-ajax-url               |
+------------------------+-----------------------------+

Another significant change is how you check on the server side if the request is indeed an AJAX request. On previous versions we simply used Request.IsAjaxRequest().

On MVC6, you have to create a simple extension to add the same options that existed on previous MVC versions (original source):

/// <summary>
/// Determines whether the specified HTTP request is an AJAX request.
/// </summary>
/// 
/// <returns>
/// true if the specified HTTP request is an AJAX request; otherwise, false.
/// </returns>
/// <param name="request">The HTTP request.</param><exception cref="T:System.ArgumentNullException">The <paramref name="request"/> parameter is null (Nothing in Visual Basic).</exception>
public static bool IsAjaxRequest(this HttpRequest request)
{
  if (request == null)
    throw new ArgumentNullException("request");

  if (request.Headers != null)
    return request.Headers["X-Requested-With"] == "XMLHttpRequest";
  return false;
}

Here's a really nice YouTube tutorial on AJAX forms, and you can download the project from this GitHub link. It contain the script to be used for AJAX.

Sample style copied from the above project:

<form asp-controller="Home1" asp-action="SaveForm" 
      data-ajax="true" 
      data-ajax-method="POST"
      data-ajax-mode="replace" 
      data-ajax-update="#content"
      data-ajax-loading  ="#divloading"
      data-ajax-success="Success"
      data-ajax-failure ="Failure">
    <div class="form-group">
        <div>  <h4>@Html.Label("Name")</h4> </div>
        <div>  @Html.TextBox("Name","",htmlAttributes:new { @class="form-control",id="Name"})</div>
    </div>
    <div class="form-group">
        <div><h4>@Html.Label("Age")</h4></div>
        <div>@Html.TextBox("Age", "", htmlAttributes: new { @class = "form-control", id ="Age" })</div>
    </div>
    <br/>
    <input type="submit" name="Submit"  class="btn btn-block btn-success" />
</form>

https://github.com/Behrouz-Goudarzi/AjaxTagHelper

AjaxTagHelper

A simple solution to using links and ajax forms using Tag Helper in aspnet core

First, copy the AjaxTagHelper class from the Extensions folder to your project.

Second, copy the AjaxTagHelper.js file from js folder in wwwroot and add it to your project.

Then do the following: Open the viewImports file and add the following code

@using AjaxTagHelper.Extensions
@using AjaxTagHelper
@using AjaxTagHelper.Models
@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
@addTagHelper *, AjaxTagHelper

To use Action Ajax, add the following code instead of the tag.

  <ajax-action ajax-action="Delete" ajax-controller="Home" ajax-data-id="@Model.Id"
                 class="btn btn-danger btn-sm" ajax-success-func="SuccessDelete">
        Delete
    </ajax-action>

Use the following code to use AJAX to send the form to server.

<div class="row">
    <form id="frmCreate" class="col-sm-9">
        <div class="row">
            <div class="col-sm-4 form-control">
                <input placeholder="Enter Name" name="Name" class="input-group" type="text" />
            </div>
            <div class="col-sm-4 form-control">
                <input placeholder="Enter Family" name="Family" class="input-group" type="text" />
            </div>
            <div class="col-sm-4 form-control">
                <input placeholder="Enter Email@site.com " name="Email" class="input-group" type="email" />
            </div>
        </div>
    </form>
    <div class="col-sm-3">
        <ajax-button ajax-controller="Home" ajax-action="Create" ajax-form-id="frmCreate" ajax-success-func="SuccessCreate"
                     class="btn btn-sm btn-success">
            Create
        </ajax-button>
    </div>
</div>

Finally, add the scripts you need to view it, check the code below

<script>
    function SuccessCreate(data) {
        console.log(data);
        $("#tbodyPerson").append(data);


    }
    function SuccessDelete(data) {
        $("#tr" + data.id).fadeOut();
    }
</script>
<script src="~/js/AjaxHelper.js"></script>