What is the reason for getting undefined when using nested 'for' loop in Javascript with Array.length?

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The reason for getting undefined when using nested 'for' loop in Javascript with Array.length is that the loop may be iterating beyond the length of the array, resulting in accessing an index that does not exist in the array. This can cause the loop to return undefined or null instead of the expected value. It is important to ensure that the loop variables are within the range of the array length to avoid this issue.