Painful JavaScript syntax features_Basic knowledge

I saw some test questions related to JavaScript posted by someone on Zhihu, and I would like to share them with you. Although it was a long time ago, these questions are quite classic, which makes people think that JavaScript is really a painful language. .

1.

Copy code The code is as follows:

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

A. "object"
B. "array"
C. "arguments"
D. "undefined"

Answer: A

2.

Copy code The code is as follows:

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

A. "number"
          B. "undefined"
C. "function"
D. Eerror

Answer: D

3.

Copy code The code is as follows:

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

A. 1
          B. null
C. undefined
D. Error

Answer: A

4.

Copy code The code is as follows:

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

A. 1
          B. "number"
C. undefined
D. "undefined"

Answer: D

5.

Copy code The code is as follows:

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

A. "number"
          B. "undefined"
C. "function"
D. Error

Answer: A

6.

Copy code The code is as follows:

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

A. "undefined"
          B. "object"
C. "number"
D. "function"

Answer: A

7.

Copy code The code is as follows:

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

A. "undefined"
          B. "object"
C. "number"
D. "function"

Answer: A

8.

Copy code The code is as follows:

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

A. "string"
          B. "number"
C. "function"
D. "undefined"

Answer: B

9.

Copy code The code is as follows:

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

A. 1
B. "1function"
C. "1undefined"
D. NaN

Answer: C

10.

Copy code The code is as follows:

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

A. "number"
          B. "string"
C. "undefined"
D. "object"

Answer: B

11.

Copy code The code is as follows:

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

A. “undefined”
           B. “object”
C. “number”
D. Error

Answer: A

12.

Copy code The code is as follows:

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

A、1
          B. 2
C. Error (e.g. “Too much recursion”)
D、undefined

Answer: B

13.

Copy code The code is as follows:

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

A. true
B、false

Answer: B

14.

Copy code The code is as follows:

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

A、1
          B. 2
C、undefined
D. Error

Answer: B

15.

Copy code The code is as follows:

Which of the following statements will generate a runtime error: ()            
A.var obj = ();    
B.var obj = []; 
C.var obj = {}; 
D.var obj = //;

Answer: A