Question

I seem to have found an undocumented breaking change in jQuery 1.8.3.

While upgrading a page from jQuery 1.7 to 1.8.3 one of our ajax calls of type “HEAD” stopped working.

Upon debugging the success callback is fired but the parameter, “xhr” is null when I use the google CDN to run the page in jQuery 1.8.3.

If I switch back to 1.7 the xhr object is fully operational and not null.

I have scoured google and jQuery site for breaking changes in 1.8.* but can find nothing on point. I need to upgrade this as another library I need to use requires the latest jQuery so I am now between a rock and a hard place.

Code is as follows:

$.ajax({
    type: "HEAD",
    async: false,
    cache: false,
    url: pth + b,
    error: function (xhr) {

    // always succeeds

    },
    success: function (xhr) {
        // in jQuery 1.7.0 ONLY xhr is a non-null object - 1.8.3/1.9.0 receive a null object as a parameter
        c = xhr.getResponseHeader('x-amz-meta-mix');
        if (c == null) c = b;

    }
});

Thanks!

PS- I should add that in Fiddler the response is always 200 and the information I am looking for is always present. The issue is that the xhr object is null if I do not use jQuery 1.7.0 in favor of 1.8.3 or 1.9.0

Answer 1

It seems that jQuery has changed the format of the success callback. In 1.8 and later it is:

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

The jqXHR is now the third argument, rather than the first, so change your success handler to:

success: function (data, status, xhr) {
    ...