jQuery.ajax，成功：函数（数据）不返回plainObject

Question

According to the documentation of Jquery.ajax success is a delegate (well at least I think it is, It lets you define the function to call) which will call a function and pass it a

PlainObject, String, jqXHR

But when I use the following code I am getting that that xml is NOT a PlainObject when I use alert to check.

$(document).ready(function () {
    $("#dvContent").append("<ul></ul>");
    $.ajax({
        type: "GET",
        url: "message.xml",
        dataType: "xml",
        success: function (xml) {
            alert(jQuery.isPlainObject(xml));
            alert(jQuery.isPlainObject($(xml)));
            $(xml).find('Book').each(function () {

                var sTitle = $(this).find('Title').text();
                var sPublisher = $(this).find('Publisher').text();
            });
        },
        error: function () {
            alert("An error occurred while processing XML file.");
        }
    });
});

How is this possible?

Answer 1

That's the nature of a dynamic language. Even though the documentation suggests that it will be PlainObject , this is not enforceable by the language. So because the content type which came back was xml and not something that can evaluated as a PlainObject .

The following question details a bit more about the isPlainObject function: IsPlainObject, thing?

From the jQuery documentation, the crucial bit is that it will be

success:

Type: Function( PlainObject data, String textStatus, jqXHR jqXHR )

The function gets passed three arguments: The data returned from the server, formatted according to the dataType parameter ;...

So by saying describing it in the method signature as PlainObject , they are saying that (if possible) it will be evaluated into a real javascript object, otherwise, you're on your own and it's the raw response from the server.