几个变态的JS问题

最新推荐文章于 2022-02-19 22:17:26 发布

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#面试题

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该博客包含21道JavaScript面试题，涉及变量提升、闭包、作用域、函数参数传递等知识点。通过代码示例展示问题，并在注释中给出部分题目的答案及相关分析，有助于深入理解JavaScript的特性和机制。

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<!DOCTYPE html>

<head>

<title>Document</title>

</head>

<body>

// 1--------------------------- **

if (!("a" in window)) {

var a = 1;

}

console.log(a);

document.write(a);

// 2------------------------------- **

console.log(a);

var a = 12;

function fn() {

console.log(a);

var a = 13;

}

fn();

console.log(a);

// 3---------------------------------------- *

console.log(a);

var a = 12;

function fn() {

console.log(a);

a = 13;

}

fn();

console.log(a);

// 4----------------------------------------- **

console.log(a);

a = 12;

function fn() {

console.log(a);

a = 13;

}

fn();

console.log(a);

// 5------------------------------------ **

var foo = 1;

function bar() {

if (!foo) {

var foo = 10;

}

console.log(foo);

}

bar();

// 6--------------------------- ,变态等级***星

var n = 0;

function a() {

var n = 10;

function b() {

n++;

console.log(n);

}

b();

return b;

}

var c = a();

c();

console.log(n);

// 7--------------------------- *

var a = 10,

b = 11,

c = 12;

function test(a) {

a = 1;

var b = 2;

c = 3;

}

test(10);

console.log(a);

console.log(b);

console.log(c);

// 8----------------------

var a = 4;

function b(x, y, a) {

console.log(a);

arguments[2] = 10;

console.log(a);

}

a = b(1, 2, 3);

console.log(a);

// 9-----------------------------------

function fn(x, y) {

var arg = arguments;

arg[0] = 100;

console.log(x);

y = 200;

console.log(arg[1]);

}

fn(10);

// 10------------------------------------****

var num = 10;

var obj = { num: 20 };

obj.fn = (function(num) {

this.num = num * 3; //WIN:60

num++; //21

return function(n) {

this.num += n;

num++;

console.log(num);

};

})(obj.num);

var fn = obj.fn;

fn(5); //65

obj.fn(10); //

console.log(num, obj.num);

// 11---------------------------------- ***

var num = 10;

obj = { num: 20 };

obj.fn = (function(num) {

num = this.num + 10;

this.num = num + 10; //WIN:30 num:20

return function() {

this.num += ++num; //win:51

};

})(num);

var fn = obj.fn;

fn();

obj.fn();

console.log(num, obj.num);

// 12---------------------------------****

function Fn() {

var n = 10;

this.m = 20;

this.aa = function() {

console.log(this.m);

};

}

Fn.prototype.bb = function() {

console.log(this.n);

};

var f1 = new Fn();

Fn.prototype = {

aa: function() {

console.log(this.m + 10);

}

};

var f2 = new Fn();

console.log(f1.constructor);

console.log(f2.constructor);

f1.bb();

f1.aa();

f2.bb();

f2.aa();

f2.__proto__.aa();

// 13-------------------------------**

var a = 12,

b = 13,

c = 14;

function fn(a) {

console.log(a, b, c);

var b = (c = a = 20);

console.log(a, b, c);

}

fn(a);

console.log(a, b, c);

// 14------------------------------------*** 函数参数为引用类型时，传递其类型的引用（指针）。函数中的局部变量

var ary = [12, 23];

function fn(ary) {

console.log(ary);

ary[0] = 100;

ary = [100];

ary[0] = 0;

console.log(ary);

}

fn(ary);

console.log(ary);

// 15----------------------------**

var n = 10;

function fn() {

var n = 20;

function f() {

n++;

console.log(n);

}

f();

return f;

}

var x = fn();

x();

console.log(n);

// 16-------------------------------------***闭包问题

var i = 1;

function fn(i) {

return function(n) {

console.log(n + ++i);

};

}

var f = fn(2);

f(3);

fn(5)(6);

fn(7)(8);

f(4);

// 17-------------------------------**栈内存释放问题

var a = 9;

function fn() {

a = 0;

return function(b) {

return b + a++;

};

}

var f = fn();

console.log(f(5));

console.log(fn()(5));

console.log(f(5));

console.log(a);

// 18---------------------------------**

function fn(i) {

return function(n) {

console.log(n + ++i);

};

}

var f = fn(10);

f(20);

fn(20)(40);

fn(30)(50);

f(30);

//19------------------------------*

var i = 10;

function fn() {

return function(n) {

console.log(n + ++i);

};

}

var f = fn();

f(20);

fn()(20);

fn()(30);

f(30);

// 20--------------------------------------****

// 变量（函数）提升后，在代码从上到下顺序执行时，在遇到方法（function）跳过不会执行

function Foo() {

getName = function() {

console.log(1);

};

return this;

}

Foo.getName = function() {

console.log(2);

};

Foo.prototype.getName = function() {

console.log(3);

};

var getName = function() {

console.log(4);

};

//下面代码到这不执行，已经全部提升

function getName() {

console.log(5);

}

Foo.getName();

getName();

Foo().getName();

getName();

new Foo.getName();

new Foo().getName();

new new Foo().getName();

// 21----------------------------------*****（逆天题）

function fn1(){console.log(1);}

function fn2(){console.log(2);}

fn1.call(fn2);

fn1.call.call(fn2);

Function.prototype.call(fn1);

Function.prototype.call.call(fn1);

</script>

<!-- <script>

function fn(){ var a = 1,b= 1; return a+b}

var ff = fn;

document.write(ff);

</script> -->

</body>

<!--

前段面试题讲解--

1:undefined; 2:undefined undefined 12; 3:undefined 12 13; 4:error; 5:10;

6:11 12 0 ; 7:10 11 3; 8:3 10 undefined;

9:100 undefined arg（arguments这个伪数组）以索引为基础，

“映射时”不存在的不予关联 arguments的映射机制建立在与函数形参赋值的一瞬间

10:22 23 (全局下的num):65 (obj中的num):30

11： 51 42；

12: Fn Object undefined 20 报错 20 NaN

16: 私有作用域以及内存释放

-->

</html>