Question

As shown in the image, I just do inArray on an array, looking for a node. and $previously_selected_node and the item at index 37 in $shapes are the same object…. so… why isn’t it working?

EDIT:
I found another way to search after one of the aswerers postedd his answer:

var result = -1;
jQuery.each(shapes, function(key, value){
    if (value.id == shape.id){
        result = key;
    }
});
return result;

apparently, part of my problem is that I can’t return in the middle of a loop. (I was returning the instant a match was found, which was causing some issues.)

Answer 1

Your object is not an array.
$.inArray only work on array-like objects with a length and a set of properties named 0 through length – 1.

You need to search your non-array manually.
For example, you could use a for / in loop to loop through all properties that actually exist and see if any of them match your object:

for (var key in $shapes) {
    if ($shapes[key] === yourObject) {
        //Match!
    }
}