Question

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Objects vs arrays in Javascript for key/value pairs

I have a variable in JavaScript which I am using like a hash. I can initialize it like:

var selected = [];

or

var selected = {};

and it does the same exact thing. I’m using it like this for example:

selected["one"] = 1;

if (selected["one"] == 1) console.log("one is selected"); 
// result: one is selected

if (selected["two"] != 1) console.log("two is not selected");
// result: two is not selected

selected["one"] = 0;

if (selected["one"] != 1) console.log("one is no longer selected");
// result: one is no longer selected

Is there really a difference? Is one an object and the other an array ? If so, when should I expect to run into problems. Ie., what is the difference between the two in their usage, and why would you chose one over the other?

Answer 1

[] is an array, {} is an object. An array is a type of object intended to be only assigned numeric keys.

While you can in theory use them interchangably, look what happens when you JSON-ify them:

var tmp = []; // or: var tmp = {}
tmp.one = 1;
JSON.stringify(tmp);

// array:
'[]'

// object:
'{"one":1}'