Javascript Array Intersect

var alpha = [1, 2, 3, 4, 5, 6],
    beta = [4, 5, 6, 7, 8, 9];

$.arrayIntersect = function(a, b)
{
    return $.grep(a, function(i)
    {
        return $.inArray(i, b) > -1;
    });
};

window.console && console.log( $.arrayIntersect(alpha, beta) );