ie gives "...is null or not an object" errors when accessing an object?

I've got a JavaScript object literal:

var things = {
    "a": {
        7: {
            "b": "asdf",
            "z": {
                1: {
                    "name": "Ship0",
                    "loa": 100,
                    "draft": 5000
                },
                2: {
                    "name": "Ship1",
                    "loa": 100,
                    "draft": 5000
                }
            }
        },
        8: {
            "b": "fdsa",
            "z": {
                5: {
                    "name": "Ship0",
                    "loa": 100,
                    "draft": 5000
                },
                6: {
                    "name": "Ship1",
                    "loa": 100,
                    "draft": 5000
                }
            }
       开发者_如何转开发 }
    }
};

... and later in a function, I do this:

function p_get_index_of_existing_ship(customer_id, ship_id)
{
    return someotherfunctionof(ship_id, things["a"][customer_id]["z"]);
}

It works nicely in firefox, but in IE(7,8) I get "error: 'things.a[...].z' is null or not an object.

Is that not the right way to access such associative arrays (objects) in javascript?

---

The keys of object literals must be valid identifier names. Your keys are 7 and 8 which are not valid names (because the first (and only) character is a digit). I suggest using strings instead:

"7": { ... }

Edit: I looked up the spec... It seems that numeric literals are valid names for keys... but it still could be that IE doesn't like them. Try strings and you'll know.

Edit: Try this:

function p_get_index_of_existing_ship(customer_id, ship_id)
{
    // return someotherfunctionof(ship_id, things["a"][customer_id]["z"]);
    things["a"][customer_id]["z"];
}

Does the error still show in IE?

---

The problem is ...[customer_id] evaluates to undefined.

Now, figure out why.