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

Question

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

namespace = new RegExp(\"(^|\\\\.)\" +
  jQuery.map( namespaces.slice(0).sort(), fcleanu         


        

Answer 1

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)