in most cases，If we want to get the contents of a section of the array (for example, front-to-middle，Some of the values of the array or the last)，This time you need to traverse the array to assign a new array：
Such an array of short, better said it does not matter，However, if the array is relatively large and we need to value and more，It is clear that it is a waste of time to traverse up。[……]