Overload functions or methods by the types of the arguments

example.js

// Simple use

var fn = Function.overload([
    ['string', 'number', function(name, age){
        return name + ' is ' + age + ' years old';
    }],
    [String, function(name){
        return 'it is just ' + name;
    }]
]);

console.log(fn('arian'));
console.log(fn('arian', 20));
console.log(fn(34));

// it is just arian
// arian is 20 years old
// null


// Using with Class

var Person = new Class({
    initialize: Function.overload([
        ['string', 'string', function(first, last){
            this.first = first;
            this.last = last;
            console.log('first: ' + first +' and last: ' + last);
        }],
        ['string', Number, function(last, age){
            this.last = last;
            this.age = age;
            console.log('Just the last name: ' + last + ' and you are ' + age + ' years old');
        }],
        function(){
            // throw Error('pass at least your last name');
        }
    ])    
});


new Person('Arian', 'Stolwijk');
new Person('Stolwijk', 20);
new Person();

// first: Arian and last: Stolwijk
// Just the last name: Stolwijk and you are 20 years old
// Uncaught TypeError: pass at least your last name

Function.overload.js

Function.overload = function(fns, thisArg){
    var dflt = (typeOf(fns[fns.length - 1]) == 'function') ? fns.pop() : null;
    return function(){
        var args = Array.from(arguments),
            self = thisArg || this;
        
        overload: for (var i = 0, l = fns.length; i < l; i++){
            var types = fns[i].slice(0, -1), length = types.length,
                fn = fns[i][length];

            if (length != args.length) continue;
            
            for (var j = length; j--;){
                if (
                    !(instanceOf(types[j], Type) && instanceOf(args[j], types[j]))
                    && typeOf(args[j]) != types[j]
                ) continue overload;
            }
            
            return fn.apply(self, args);
        }
        return dflt && dflt.apply(self, args);
    };
};

this is really cool