トグル処理

function toggle(){
    var fn = arguments;
    var l = arguments.length;
    var i = 0;
    return function(){
        if(l <= i) i=0;
        fn[i++]();            
    }
}

function a1(){
  console.log('Hello');
}
function a2(){
  console.log('World');
}
function a3(){
  console.log('hoge');
}

var b = toggle(a1, a2);
b() -> Hello
b() -> World
b() -> Hello
b() -> World

var c = toggle(a1, a2, a3);
c() -> Hello
c() -> World
c() -> hoge
c() -> Hello