Proper subset function for MongoDB $where clause

subset.js

// Define function
subset = function (test, superset) {
    if (test.length > superset.length) {
        return false;
    }
    for (var i in test) {
        found = false;
        for (var j in superset) {
            found = found || superset[j] == test[i];
        }
        if (!found) {
            return false;
        }
    }
    return true;
}

// Save function to the server, only needs to be done once.
db.system.js.save( { _id : "subset", value : subset } )

db.coll.find({ $where : "subset(this.attr, [2,3,4])" })  // subsets of 2,3,4
db.coll.find({ $where : "! subset(this.attr, [2,3,4])" }) // not subset of 2,3,4