[austincheney]

As an interesting fun fact many languages, including JavaScript, inherit complex type memory organization from C lang. So the same fundamental performance implications work the same way in all these related languages, because it is more about what happens on the metal than at the syntax.

Please note this observation only applies to access during execution.

During the late 70s a developer named Paul Heckel discovered that hash maps (what JavaScript objects are) were randomly accessed in memory until the specified key was found. That random access was faster than the access of a specified index from an array, because array indexes are accessed sequentially. Because arrays are ordered sequentially, even in memory, they are substantially faster to iterate over, though.

http://documents.scribd.com/docs/10ro9oowpo1h81pgh1as.pdf

Interesting (and unexpected): I tried searching for "Paul Heckel" in Google and only found stuff about a jazz musician. Then I searched for "Paul Heckel's algorithm" and my writing about implementing the algoritm in JavaScript was one of the first Google results.