Rails to_sentence implemented in JavaScrip

toSentence.js

/* Given an array of strings it returns a sentence. */
function toSentence(arr) {
    arr = arr.slice(0);
    switch (arr.length) {
        case 0:
            return "";
        case 1:
            return arr.pop();
        default:
            var lastItem = arr.pop();
            return arr.join(', ') + " and " + lastItem;
    }
}