Factory function example

gistfile1.js

function inherit(p) {
    if (p == null)
        throw TypeError();
    if (Object.create)
        return Object.create(p);
    var t = typeof p;
    if (t !== "object" && t !== "function")
        throw TypeError();
    function f() {}; 
    f.prototype = p;
    return new f();
}

// factory function
function range(from, to) {
    var r = inherit(range.methods);
    r.from = from;
    r.to = to; 
    return r;
}

// prototype object
range.methods = { 
    includes: function (x) {
        return this.from <= x && x <= this.to;
    },  
    foreach: function (f) {
        for (var x = Math.ceil(this.from); x <= this.to; x++)
            f(x);
    },  
    toString: function () {
        return "(" + this.from + "..." + this.to + ")";
    }   
}

var r = range(1, 3);
r.includes(2);
r.foreach(console.log);
console.log(r);