Array is not local scope inside function?

I’ve noticed a JavaScript behavior that does not agree with my understanding of variable scope and was hoping that someone could clarify:

[CODE]function change(arr)
{
var tmp1 = arr[0];
var tmp2 = arr[1];
arr[0] = arr[2];
arr[1] = tmp1;
arr[2] = tmp2;
}

var arr = [‘cat’, ‘dog’, ‘parrot’];

change(arr);

alert(arr.join(‘,’)); //results in “parrot, dog, cat”[/CODE]

In the above code, the function accepts an array, puts the third item at the beginning, and moves the other two to the right. If you’ll notice, however, the function does [I]not[/I] return the newly sorted array. It simply operates on the array it was given, which in my understanding should be an entirely independent array with scope that is [I]local[/I] to the function and ceasing to exist when the function stops executing.

So how come the resulting alert is “parrot, dog, cat?” Even though the function operated only on the array it was given, it affected the original array.

Note that in this example the original array is [I]not[/I] changed:

[CODE]function change(arr)
{
arr = [‘monkey’, ‘mouse’, ‘ferret’];
}

var arr = [‘cat’, ‘dog’, ‘parrot’];

change(arr);

alert(arr.join(‘,’)); //This time, alert is “cat, dog, parrot.”[/CODE]

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