Last array element

Returns the last element in an array.

• Check if arr is truthy and has a length property.
• Use Array.prototype.length to compute the index of the last element of the given array and return it, otherwise return undefined.

const last = arr => (arr && arr.length ? arr[arr.length - 1] : undefined);

last([1, 2, 3]); // 3
last([]); // undefined
last(null); // undefined
last(undefined); // undefined