That gives you the first (and only) item from the sliced array, which is then passed to the alert(.). Moving left-to-right, we now have an array of a single item followed by an array index. So, array.slice(-1) gives you an array containing the last element from the original array. slice(-2) extracts the last two elements in the sequence.Ī new array containing the extracted elements. Both function calls and member access are level 19, with left-to-right associativity, which means we evaluate the function call first, then the array index next.įor this, let's turn to the documentation on array.slice, which says:Ī negative index can be used, indicating an offset from the end of the sequence. Which is evaluated first? To answer this, we turn to Operator Precedence.

It has one argument: array.slice(-1), which we'll examine next.Īrray.slice(-1) is another function call. Before it can execute (and print something to the screen), its arguments must be evaluated first. This is your original statement: alert(array.slice(-1)) Īlert(.) is a function call. By understanding each small piece, you will understand the whole.

Break the expression down into its parts.

Js array slice