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Asked: 2026-05-10T13:57:09+00:00

What could be the problem with reversing the array of DOM objects as in

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What could be the problem with reversing the array of DOM objects as in the following code:

var imagesArr = new Array(); imagesArr = document.getElementById('myDivHolderId').getElementsByTagName('img'); imagesArr.reverse();

In Firefox 3, when I call the reverse() method the script stops executing and shows the following error in the console of the Web Developer Toolbar:

imagesArr.reverse is not a function

The imagesArr variable can be iterated through with a for loop and elements like imagesArr[i] can be accessed, so why is it not seen as an array when calling the reverse() method?

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1 Answer

  1. Because getElementsByTag name actually returns a NodeList structure. It has similar array like indexing properties for syntactic convenience, but it is not an array. For example, the set of entries is actually constantly being dynamically updated – if you add a new img tag under myDivHolderId, it will automatically appear in imagesArr.

    See http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-536297177 for more.

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