Question

Which one is faster: iterating over a an array or an object. And what happens when i need to perform action such as deleting any element from in between?

var a = {"A1":1, "B1":2, "C1":3};

or

var a = ["A1", "B1", "C1"];

Answer 1

Iterating over arrays should be faster than iterating over an object, but it’ll depend on:

1. the size of the object / array
2. whether your keys are contigious
3. all sorts of other optimiser crap

On older browsers, removing elements from an array used to be very expensive (because it required changing the key on every subsequent element) but on modern browsers that’s less of a problem.

Seriously, just use whichever is the best representation for your project, and then worry about optimisation later if it becomes a problem.