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Array.length remains the same even though array has element index greater than length set: Bug or feature?

kangjiahuang2007
kangjiahuang2007
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I don't really know if this is a bug, or a feature of Firefox's JavaScript core engine. Say I have an array:

var array = [];

I set the length of the array to a very large number:

array.length = 155555555;

This now turns the variable array into an array with 155555555 blank slots. If I then do:

array[502039410402] = 5; // Notice that 502039410402 > the previously set 155555555 for length

array.length remains at 155555555, but the actual array is appended with a sudden index 502039410402 (i.e., index 155555553, 155555554, and then suddenly index 502039410402; see screenshot), with that element containing 5. Is this a bug, or an intended feature?

I would appreciate it if anyone could let me know.

Thanks!

I don't really know if this is a bug, or a feature of Firefox's JavaScript core engine. Say I have an array: var array = []; I set the length of the array to a very large number: array.length = 155555555; This now turns the variable array into an array with 155555555 blank slots. If I then do: array[502039410402] = 5; // Notice that 502039410402 > the previously set 155555555 for length array.length remains at 155555555, but the actual array is appended with a sudden index 502039410402 (i.e., index 155555553, 155555554, and then suddenly index 502039410402; see screenshot), with that element containing 5. Is this a bug, or an intended feature? I would appreciate it if anyone could let me know. Thanks!
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All Replies (2)

cor-el
cor-el
  • Moderator
  • Top 10 Contributor
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The values you use are very large.

Can you replicate this with small values like 50 and 100 and if not, when does it stop working ?

jscher2000 - Support Volunteer
jscher2000 - Support Volunteer
  • Top 25 Contributor
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Oh no, array.length isn't read-only? Why, JavaScript, why?! But setting that aside...

The MDN article says length must be less than 232 (4294967296).

Elements with indexes beyond that size seem to exist in a state of limbo, and don't behave like members of the array in array operations:

I've read many times that everything in JavaScript is an object, so perhaps that's why the limbo elements can exist.