data structures - Objects vs arrays in Javascript for key/value pairs

Question

Say you have a very simple data structure:

(personId, name)

...and you want to store a number of these in a javascript variable. As I see it you have three options:

// a single object
var people = {
    1 : 'Joe',
    3 : 'Sam',
    8 : 'Eve'
};

// or, an array of objects
var people = [
    { id: 1, name: 'Joe'},
    { id: 3, name: 'Sam'},
    { id: 8, name: 'Eve'}
];

// or, a combination of the two
var people = {
    1 : { id: 1, name: 'Joe'},
    3 : { id: 3, name: 'Sam'},
    8 : { id: 8, name: 'Eve'}
};

The second or third option is obviously the way to go if you have (or expect that you might have) more than one "value" part to store (eg, adding in their age or something), so, for the sake of argument, let's assume that there's never ever going to be any more data values needed in this structure. Which one do you choose and why?

---

Edit: The example now shows the most common situation: non-sequential ids.

Answer 1

Each solution has its use cases.

I think the first solution is good if you're trying to define a one-to-one relationship (such as a simple mapping), especially if you need to use the key as a lookup key.

The second solution feels the most robust to me in general, and I'd probably use it if I didn't need a fast lookup key:

• It's self-describing, so you don't have to depend on anyone using people to know that the key is the id of the user.
• Each object comes self-contained, which is better for passing the data elsewhere - instead of two parameters (id and name) you just pass around people.
• This is a rare problem, but sometimes the key values may not be valid to use as keys. For example, I once wanted to map string conversions (e.g., ":" to ">"), but since ":" isn't a valid variable name I had to use the second method.
• It's easily extensible, in case somewhere along the line you need to add more data to some (or all) users. (Sorry, I know about your "for argument's sake" but this is an important aspect.)

The third would be good if you need fast lookup time + some of the advantages listed above (passing the data around, self-describing). However, if you don't need the fast lookup time, it's a lot more cumbersome. Also, either way, you run the risk of error if the id in the object somehow varies from the id in people.