[转] 考验你的JavaScript底细

http://sentsin.com/

尽管今日的JavaScript已经突飞猛进，但JS的许多特性仍然保留，以下题目并不是有意设坑，许多地方将验证你的JS底细，如果错了一半，请别告诉我你从事前端。

1.

(function(){
return typeof arguments;
})();

"object"

"array"

"arguments"

"undefined"

2.

var f = function g(){
return 23;
};
typeof g();

"number"

"undefined"

"function"

Error

3.

(function(x){
delete x;
return x;
})(1);

1

null

undefined

Error

4.

var y = 1, x = y = typeof x;
x;

1

"number"

undefined

"undefined"

5.

(function f(f){
return typeof f();
})(function(){ return 1; });

"number"

"undefined"

"function"

Error

6.

var foo = {
bar: function() {
return this.baz;
},
baz: 1
};
(function(){
return typeof arguments[0]();
})(foo.bar);

"undefined"

"object"

"number"

"function"

7.

var foo = {
bar: function(){
return this.baz;
},
baz: 1
}
typeof (f = foo.bar)();

"undefined"

"object"

"number"

"function"

8.

var f = (
function f(){
return "1";
},
function g(){
return 2;
}
)();
typeof f;

"string"

"number"

"function"

"undefined"

9.

var x = 1;
if (function f(){}) {
x += typeof f;
}
x;

1

"1function"

"1undefined"

NaN

10.

var x = [typeof x, typeof y][1];
typeof typeof x;

"number"

"string"

"undefined"

"object"

11.

(function(foo){
return typeof foo.bar;
})({ foo: { bar: 1 } });

"undefined"

"object"

"number"

Error

12.

(function f(){
function f(){ return 1; }
return f();
function f(){ return 2; }
})();

1

2

Error (e.g. "Too much recursion")

undefined

13.

function f(){ return f; }
new f() instanceof f;

true

false

14.

with (function(x, undefined){}) length;

1

2

undefined

Error

思考题：
如何改变 undefined的typeof类型 ? （即 typeof undefined 或者 typeof(undefined) 都不为"undefined" ）