Javascript Array groupJoin(arr, outer, inner, result, comparer)

Array.prototype.groupJoin = function (arr, outer, inner, result, comparer) {
    comparer = comparer || EqualityComparer;
    return this/* w  ww .j av a  2 s .co  m*/
    .select(function (t) {
        var key = outer(t);
        return {
            outer: t,
            inner: arr.where(function (u) { return comparer(key, inner(u)); }),
            key: key
        };
    })
    .select(function (t) {
        t.inner.key = t.key;
        return result(t.outer, t.inner);
    });
};