Method/Function Overloading in JavaScript

/**
 * Method/Function Overloading
 *
 * A way of mapping a single function call to multiple functions based upon the
 * arguments they accept.
 *
 * @Reference:
 * http://ejohn.org/blog/javascript-method-overloading/
 * http://ejohn.org/apps/learn/#90
 *
 * Explanation:
 * http://stackoverflow.com/a/30989908/1672655
 * http://stackoverflow.com/a/18122417/1672655
 *
 * Best practises:
 * http://stackoverflow.com/questions/456177/function-overloading-in-javascript-best-practices
 */

function addMethod(object, name, fn) {
    var old = object[name];
    // Get the old function corresponding to this name. Will be "undefined"
    // the first time "addMethod" is called.

    object[name] = function() {
        // Now, assign object[name] to a new function.
        // The critical part of this function is that "old" is captured inside of
        // this function and will be available any time the function is called.

        if (fn.length == arguments.length) {
            // if the number of parameters belonging to the function we've added
            // matches what was passed in, call "fn"
            return fn.apply(this, arguments);
        } else if (typeof old == "function") {
            // Otherwise if there's another function with this name
            // call it instead.
            return old.apply(this, arguments);
        }
    };
}

function Ninjas() {
    var ninjas = ["Dean Edwards", "Sam Stephenson", "Alex Russell"];

    addMethod(this, "find", function() {
        return ninjas;
    });

    addMethod(this, "find", function(name) {
        var ret = [];
        for (var i = 0; i < ninjas.length; i++)
            if (ninjas[i].indexOf(name) == 0) ret.push(ninjas[i]);
        return ret;
    });

    addMethod(this, "find", function(first, last) {
        var ret = [];
        for (var i = 0; i < ninjas.length; i++)
            if (ninjas[i] == first + " " + last) ret.push(ninjas[i]);
        return ret;
    });
}

//  USAGE
//
//  var ninjas = new Ninjas();
//  ninjas.find().length == 3
//  ninjas.find("Sam").length == 1
//  ninjas.find("Dean", "Edwards").length == 1
//  ninjas.find("Alex", "X", "Russell") == null