Question: ```
var my = {};

my["1"] = "tom";

my["2"] = "tony";

document.writeln(my["2"]);

```

A simple question, what is the {} called? I know [] is called arraylist and I can do my.indexOf() etc. on it, but this doesn't work with {}.

Where can I find a list of operation I can perform with list with {}

Answer: 
`{}` is called an object and in your declaration:

```
var my = {};

```

you are just creating an empty object to which you can then add properties to. 

Both arrays and objects can be accessed with the `[x]` syntax. Arrays are best used for sequential access with numeric indexes as in:

```
x[1]
x[2]

```

Objects are best used for access with non-sequential string indexes such as:

```
my["autoSaveTime"]
my.autoSaveTime

```

Some people also think of objects as a hash table or an associative array because they can often serve a similar purpose to those other programming constructs.

Per the question you asked in your comment, Arrays have properties like `.length` and methods like `.push()` and `.pop()`. Objects do not. MDN is a good source of reference information on things like this. Here's the [MDN page on array methods](https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array) and here's a [good overview on working with objects](https://developer.mozilla.org/en/JavaScript/Guide/Working_with_Objects).

Objects don't have those methods. Since objects don't have an order to them, you just assign to them or read to them or iterate them or delete a property as there is no need to try to change their order as their is with arrays.

```
var x = my.autoSaveTime;
my.autoSaveTime = 200;
for (var key in my) {
    var item = my[key];
    // do something with item or key here
}

```

One tricky thing to understand is that an Array is actually derived from an Object, with the additional array capabilities added. That is, an array can also contain arbitrary string named properties like an object and has all the generic methods that an object has. An object does not have array capabilities and methods. So, an array is a superset of an object.
an "Object"
<http://www.dyn-web.com/tutorials/obj_lit.php>