前端奇葩题！！！！！

(function(){
    (function(){
        console.log(123);
    }());

    setTimeout(arguments.call,1000);
}());
//123


for(var i=0;i<3;i++){
    setTimeout(function(){
      console.log(i);
    },0);
}
//3,3,3


function add(a,b){
    alert(a+b);
}

function sub(a,b){
    alert(a-b);
}

add.call(sub,3,1);
// 4



var x=20;
var a={
    x:15,
    fn:function(){
        var x=30;
        return function(){
            return this.x;
        }
    }
}
console.log("a.fn():", a.fn());
console.log("(a.fn())():",(a.fn())());
console.log("a.fn()()", a.fn()());

console.log(a.fn.call(this));
console.log(a.fn().call(a));
/*
 a.fn(): function (){
 return this.x;
 }

 (a.fn())(): 20

 a.fn()() 20

 function (){
 return this.x;
 }

 15
* */