Insert and remove random JavaScript array indices

Question

I insert some elements into an array with randomly generated indexes, for example:

var myArray = new Array();
myArray[123] = "foo";
myArray[456] = "bar";
myArray[789] = "baz";
...

In other words, array indices do not start from zero, and there will be "numeric spaces" between them. My questions:

• Will these numeric spaces be allocated in some way (and therefore take some memory) even if they have no assigned values?
• When I remove myArray [456] from the top example, will the elements be moved below this element?

EDIT: Regarding my question / concern about wrapping items after insertion / deletion - I want to know what happens to memory, not indexes. Additional information from the wikipedia article :

Linked lists have several advantages over dynamic arrays. Inserting an element at a certain point in the list is a constant-time operation, whereas inserting randomly into places in a dynamic array will require you to move half the elements on average, and all elements in the worst case. Although one can "remove" an element from the array at a constant time, somehow marking its slot as "free", this causes fragmentation, which hinders the iteration performance.

Answer 1

Will these numeric spaces be allocated in some way (and therefore take some memory) even if they have no assigned values?

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obj[456] = "bar";
obj[789] = "baz";

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Answer 2

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Answer 3

“Gaps” will not lead to distribution, and no, there is no “bias” of existing values ​​from their indices.