What's the point of .slice(0) here?

I was studying the jQuery source when I found this (v1.5 line 2295):

namespace = new RegExp("(^|\\.)" +
  jQuery.map( namespaces.slice(0).sort(), fcleanup ).join("\\.(?:.*\\.)?") + "(\\.|$)");

My question is, why use slice(0) here?

sort() modifies the array it's called on - and it isn't very nice to go around mutating stuff that other code might rely on.

slice() always returns a new array - the array returned by slice(0) is identical to the input, which basically means it's a cheap way to duplicate an array.

arr.slice(0) makes a copy of the original array by taking a slice from the element at index 0 to the last element.

It's also used to convert array-like objects into arrays. For example, a DOM NodeList (returned by several DOM methods like getElementsByTagName) is not an array, but it is an array-like object with a length field and is indexable in JavaScript. To convert it to an array, one often uses:

var anchorArray = [].slice.call(document.getElementsByTagName('a'), 0)

slice(0) creates a new array identical to the original array. Many times you want to preserve your original array and create a new one.

If you use slice(1), it will create a different array starting from index position 1.

Similar things hold for strings as well.

slice(0) allows you to return an array of the existing array you're referencing, in this case namespaces.