Question

In Javascript, if I do something like

var alpha = [];
alpha[1000000] = 2;

does this waste memory somehow? I remember reading something about Javascript arrays still setting values for unspecified indices (maybe sets them to undefined?), but I think this may have had something to do with delete. I can’t really remember.

Answer 1

See this topic:
are-javascript-arrays-sparse

In most implementations of Javascript (probably all modern ones) arrays are sparse. That means no, it’s not going to allocate memory up to the maximum index.

If it’s anything like a Lua implementation there is actually an internal array and dictionary. Densely populated parts from the starting index will be stored in the array, sparse portions in the dictionary.