listAsSentence.js

/**
 * Create an English sentence string from an array of items.
 *
 * @param  {array} array           [description]
 * @param  {string} separator      Separator for list items. Defaults to ","
 * @param  {string} finalSeparator Separator for last item. Defaults to "and"
 * @return {string}                List as an English sentence.
 */
function listAsSentence(array, separator, finalSeparator)
{
    separator = separator || ',';
    finalSeparator = finalSeparator || 'and';
    var str = '';

    for (i = 0; i < array.length; i++) {
        str = str + array[i];
        if (typeof array[i + 1] !== 'undefined') {
            if (typeof array[i + 2] === 'undefined') {
                str += ' ' + finalSeparator + ' ';
            } else {
                str += separator + ' ';
            }
        }
    }

    return str;
}

listAsSentence(['a', 'b', 'c', 'd']); // a, b, c and d