jQuery AJAX - receive multiple data

I use Wordpress, PHP, jQuery and AJAX.

I can get data from PHP through an AJAX call, like this:

$.ajax({
    type: "POST",
    url: "<?php echo get_bloginfo('url'); ?>/?addmod_ajax=1",
    data: "action=load&type=part",
    success: function(data){
        alert(data);
    }
});

When I have received the data I also want to know how it went. The "data" contains HTML and I also want error codes like "success" or "not-found".

How do I solve it the best way?

Wordpress

Because I use Wordpress I need to call a AJAX trigger (in the url). If I could keep that intact it would be nice.

$.ajax({
    type: "POST",
    url: "<?php echo get_bloginfo('url'); ?>/?addmod_ajax=1",
    data: "action=load&type=part",
    success: function(data){
        alert(data);
    },
    failure: function(){
        alert('failed');
    }
});

You could add a failure handler to see if the ajax request is failed, but other than that, if want a different return value, you will have to change the result of the function you are calling on the backend, or create a new similar function that instead of just returning the html, returns a json encoded array with the first element being found or not found, and the second element being the html.

Edit: Appended comment to complete answer and format code.

at the place where you echo 'your result', you can echo instead

json_encode(array('success'=>true,'html'=>$yourData)); 

and in your ajax call, add

 dataType:'json'

then you can access the success and html values in your success handler.

I usually just return an array or dict with one value designated as the state.

$.get(url,data,function(data) {
    if (data[0]=='parseError') { //could also be data.state
         $("#formError").html("You have entered an invalid value.").show();
    }
    else if (data[0]=='permissionDenied') {
        $("#formError").html("You do not have permission to edit this.").show();
    }
    else {
        $("#formSuccess").html("Your changes have been saved");
    }
});

Those examples may not be the best (permission denied and parsing errors could be handled on the front end). Still the concept is solid.