Proxies - in this instance `__noSuchMethod__` indirect invocation on a different method. This is really powerful for wrapping native items (like array, object) and providing methods that point to libraries like underscore, squishy. This following unboxes (`extract`) the `Seq` to works on the array and then boxes the array back into a `Seq` so it…

Seq.js

/**Note: This works in Firefox Nightly but not in Chrome (shame on you!)**/
var s = {
    concat: function(a, b) {
        return a.concat(b);
    },
    map: function(a, f) {
        var accum = [],
            total,
            i;
 
        for (i = 0, total = a.length; i < total; i++) {
            accum[i] = f(a[i]);
        }
        return accum;
    },
    isArray: function(a) {
        if(Array.isArray) return Array.isArray(a);
        else return Object.prototype.toString.call(a) === "[object Array]";
    },
    extract: function(o) {
        return 'extract' in o ? o.extract() : o;
    }
};
 
function Seq(v) {
    this.value = s.isArray(v) ? v : [].slice.call(arguments);
    this.extract = function() {
        return this.value;
    };
}
Seq.create = function(v) {
    var value = s.isArray(v) ? v : [].slice.call(arguments);
    return new Proxy(new Seq(value), {
        get: function(obj, prop) {
            if (prop in obj) return obj[prop];
            else if(!(prop in s)) throw new Error('NoSuchMethod ' + prop + ' on ' + s);
            
            return function() {
                var args = s.map([].slice.call(arguments), function(a) {
                    return s.extract(a);
                });
                return Seq.create(s[prop].apply(null, [s.extract(obj)].concat(args)));
            }
        }
    });
}
 
var seq0 = Seq.create(1, 2, 3),
    seq1 = Seq.create(4, 5, 6),
    seq2 = Seq.create(7, 8, 9);
 
console.log('Fin', seq0.concat(seq1).concat(seq2).map(x => x * 2)); // Seq(2, 4, 6, 8, 10, 12, 14, 16, 18)

It's highly possible to make this a high level function so that it's possible to do this with any object.