Question

Here’s some javascript:

$.ajax({
        type: "POST",
        url: "default.aspx/GetDate",
        contentType: "application/json; charset=utf-8",
        data: {},
        dataType: "json",
        success: function(result) {
            alert(result.d);
        }
     });

The above method works as I would expect and alerts the string returned from the [WebMethod] called GetDate in default.aspx

But when I use:

$.post(
        "default.aspx/GetDate",
        {},
        function(result) {
            alert(result.d);
        },
        "json"
     );

The alert in this success method never fires.

In firebug I can see that the POST has basically worked – it returns 200 OK
But the response in this case is the HTML of the entire default.aspx page rather than the JSON returned when I use the $.ajax() method.

EDIT:
The response and request headers shown in firebug are NOT identical.

With $.ajax()…

REQUEST:
Accept  application/json, text/javascript, */*; q=0.01
Accept-Charset  ISO-8859-1,utf-8;q=0.7,*;q=0.7
Accept-Encoding gzip, deflate
Accept-Language en-gb,en;q=0.5
Connection  keep-alive
Content-Type    application/json; charset=utf-8
Cookie  (removed)
Host    (removed)
Referer (removed)
User-Agent  Mozilla/5.0 (Windows NT 6.1; WOW64; rv:9.0.1) Gecko/20100101 Firefox/9.0.1
X-Requested-With    XMLHttpRequest

RESPONSE:
Cache-Control   private, max-age=0
Content-Length  27
Content-Type    application/json; charset=utf-8
Date    Wed, 11 Jan 2012 12:36:56 GMT
Server  Microsoft-IIS/7.5
X-Powered-By    ASP.NET

With $.post()…

REQUEST:
Accept  application/json, text/javascript, */*; q=0.01
Accept-Charset  ISO-8859-1,utf-8;q=0.7,*;q=0.7
Accept-Encoding gzip, deflate
Accept-Language en-gb,en;q=0.5
Connection  keep-alive
Cookie  (removed)
Host    (removed)
Referer (removed)
User-Agent  Mozilla/5.0 (Windows NT 6.1; WOW64; rv:9.0.1) Gecko/20100101 Firefox/9.0.1
X-Requested-With    XMLHttpRequest

RESPONSE:
Cache-Control   private
Content-Length  13815
Content-Type    text/html; charset=utf-8
Date    Wed, 11 Jan 2012 12:36:53 GMT
Server  Microsoft-IIS/7.5
X-AspNet-Version    2.0.50727
X-Powered-By    ASP.NET

Can I use the the $.post() method for this, or do I have to use the $.ajax() method?

Answer 1

That’s normal. When you use $.post you cannot set contentType: 'application/json' as you do with $.ajax. And the server expects this header. So basically you cannot invoke an ASP.NET page method with $.post.