The index values are zero relative, and the elements that will end up in the new array will be from the starting index, and up to but not including the ending index.
Negative index values can be given to Array.slice this results in the corresponding index value from the end of the length of an array. So then array slice can be used as a quick way of getting the lat element of an array.
So because Array.slice returns a new Array rather than mutating one it can, in some cases, be used as a way to clone an array assuming it is an array of primitive values.
This works because I am working with an array of primitives, objects however are copied by reference.