The concat method produces a new array containing a shallow copy of this array with the items appended to it. If an item is an array, then each of its elements is appended individually. Also see array.push(item...) later in this chapter.
The join method makes a string from an array . It does this by making a string of each of the array 's elements, and then concatenating them all together with a separator between them. The default separator is ','. To join without separation, use an empty string as the separator.
The pop and push methods make an array work like a stack. The pop method removes and returns the last element in this array . If the array is empty, it returns undefined.