Format words into a sentence

JavaScript

function formatWords(words) {
    words = words.filter(function (a) {
        return (a !== '');
    });
    words = words.filter(function (a) {
        return (a !== ',');
    });
    console.log(words);
    if (words.length === 0) {
        return '';
    }
    if (words.length === 1) {
        return words[0];
    }

    var end = words.length > 2 ? ', ' + words[words.length - 2] + ' and ' + words[words.length - 1] : words[words.length - 2] + ' and ' + words[words.length - 1];
    var result = words.splice(0, words.length - 2).join(', ');
    return result + end;
}

//console.log(formatWords(['rambo', 'ninja', 'samurai', 'ronin'])); // should return "ninja, samurai and ronin"

//console.log(formatWords(['ninja', '', 'ronin'])); // should return "ninja and ronin"
console.log(formatWords(['one', 'two','', 'three','four'])); // should return ""