Making a Simple Ajax call to controller in asp.net mvc

Use a Razor to dynamically change your URL by calling your action like this:

$.ajax({
    type: "POST",
    url: '@Url.Action("ActionName", "ControllerName")',
    contentType: "application/json; charset=utf-8",
    data: { data: "yourdata" },
    dataType: "json",
    success: function(recData) { alert('Success'); },
    error: function() { alert('A error'); }
});

After the update you have done,

1. its first calling the FirstAjax action with default HttpGet request and renders the blank Html view . (Earlier you were not having it)
2. later on loading of DOM elements of that view your Ajax call get fired and displays alert.

Earlier you were only returning JSON to browser without rendering any HTML. Now it has a HTML view rendered where it can get your JSON Data.

You can't directly render JSON its plain data not HTML.

If you just need to hit C# Method on in your Ajax Call you just need to pass two matter type and url if your request is get then you just need to specify the url only. please follow the code below it's working fine.

C# Code:

    [HttpGet]
    public ActionResult FirstAjax()
    {
        return Json("chamara", JsonRequestBehavior.AllowGet);
    }   

Java Script Code if Get Request

    $.ajax({
        url: 'home/FirstAjax',
        success: function(responce){ alert(responce.data)},
        error: function(responce){ alert(responce.data)}
    });

Java Script Code if Post Request and also [HttpGet] to [HttpPost]

        $.ajax({
            url: 'home/FirstAjax',
            type:'POST',
            success: function(responce){ alert(responce)},
            error: function(responce){ alert(responce)}
        });

Note: If you FirstAjax in same controller in which your View Controller then no need for Controller name in url. like url: 'FirstAjax',

Remove the data attribute as you are not POSTING anything to the server (Your controller does not expect any parameters).

And in your AJAX Method you can use Razor and use @Url.Action rather than a static string:

$.ajax({
    url: '@Url.Action("FirstAjax", "AjaxTest")',
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    success: successFunc,
    error: errorFunc
});

From your update:

$.ajax({
    type: "POST",
    url: '@Url.Action("FirstAjax", "AjaxTest")',
    contentType: "application/json; charset=utf-8",
    data: { a: "testing" },
    dataType: "json",
    success: function() { alert('Success'); },
    error: errorFunc
});