Are Javascript arrays sparse?

Question

That is, if I use the current time as an index into the array:

array[Date.getTime()] = value;

will the interpreter instantiate all the elem

Answer 1

Javascript objects are sparse, and arrays are just specialized objects with an auto-maintained length property (which is actually one larger than the largest index, not the number of defined elements) and some additional methods. You are safe either way; use an array if you need it's extra features, and an object otherwise.