When comparing a JavaScript Array to an Object, the distinction may not seem significant. Essentially, an Array primarily introduces the length attribute, allowing both Arrays and Objects to function as numeric arrays:
var ar = new Array();
ar[0] = "foo";
ar["bar"] = "foo";
var ob = new Object();
ob[0] = "foo";
ob["bar"] = "foo";
assert(ar[0] == ob[0] == ar["0"] == ob["0"] == ar.bar == ob.bar); // Should be true.
So the question arises, how is this functionality handled in popular JavaScript engines (V8, JavaScriptCore, SpiderMonkey, etc.)? It is undesirable for arrays to be stored as hash maps with key values. How can we ensure that our data is indeed stored as a genuine array?
Several approaches could potentially be taken by these engines:
Arrayis essentially treated as an associative array with string keys, much likeObject.Arraycould have a specialized implementation with a numeric key-backed structure resemblingstd::vector, along with a density heuristic to manage memory usage when handling very large indices.Arraymight share similarities withObject, but objects could undergo a heuristic process to determine if utilizing an array would be more efficient.- A highly complex method that has not been considered yet.
Having a dedicated array type (like WebGL typed arrays) would streamline this process.