calling server function from client side

Question

I need to call a method in the code behind from client side using json, but the method never got called, and the error "c" is blank. What did I do wrong here?

Client side code:

$.ajax({
    type: "POST",
    contentType: "application/json; charset=utf-8",
    url: "MyPage.aspx/CheckItem",
    data: {item: item},
    dataType: "json",
    success: function (result) {
        if (result) {
            errorMessage.innerHTML = 'WARNING: Item exists.';
            return false;
        }
    },
    error: function (a,b,c) {
        alert("error: " + c);
    }
});

Server side code:

[System.Web.Services.WebMethod]
public static bool CheckItem(string item)
{
    DataContext dc = new DataContext();

    var record = dc.MyTable.Where(x => x.Item == item).FirstOrDefault();
    if (record != null)
        return true;
    else
        return false;
}

Answer 1

Kindly enclose your parameter with quotes/double quotes. Please see below.

            var item = 0;
            $.ajax({
                type: "POST",
                url: "/WebForm1.aspx/CheckItem",
                data: '{"item":"' + item +'"}',
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                error: function (errorThrown) {

                    alert(errorThrown.responseText + "what's wrong?" + " " + errorThrown);
                },
                success: function (msg) {

                    alert(msg.d);
                    return false;
                    // Do something interesting here.
                }
            });

    [WebMethod]
    public static bool CheckItem(string item)
    {
        return true;
    }

Answer 2

If you want to call a method in an ASP page, you're going to need to add some logic inside the ASP page to call the function. You can't just call it directly from $.ajax(). For example, your ajax call might be:

$.ajax({
    type: "POST",
    contentType: "application/json; charset=utf-8",
    url: "MyPage.aspx",
    data: {
        item: item,
        method: 'CheckItem'
    },
    dataType: "json",
    success: function (result) {
        if (result) {
            errorMessage.innerHTML = 'WARNING: Item exists.';
            return false;
        }
    },
    error: function (a,b,c) {
        alert("error: " + c);
    }
});

And then inside your asp code, you would look for the "method" form variable and call the specified method.