这些JavaScript编程黑科技

1、单行写一个评级组件

"★★★★★☆☆☆☆☆".slice(5 - rate, 10 - rate);定义一个变量rate是1到5的值，然后执行上面代码，看图

才发现插件什么的都弱爆了

2、如何装逼用代码骂别人SB

(!(~+[])+{})[--[~+""][+[]]*[~+[]] + ~~!+[]]+({}+[])[[~!+[]]*~+[]]

了解为什么请移步：一行能装逼的JavaScript代码

3、如何用代码优雅的证明自己NB

这个牛逼了

	console.log(([][[]]+[])[+!![]]+([]+{})[!+[]+!![]])

4、JavaScript 错误处理的方式的正确姿势

，舅服你

try {

    something

} catch (e) {

    window.location.href =

        "http://stackoverflow.com/search?q=[js]+" +

        e.message;

}

5、从一行代码里面学点JavaScript

[].forEach.call($$("*"),function(a){

    a.style.outline="1px solid #"+(~~(Math.random()*(1<<24))).toString(16)

})

翻译成正常语言就是这样的

Array.prototype.forEach.call(document.querySelectorAll('*'),

dom => dom.style.outline = `1px solid #${parseInt(Math.random() *

Math.pow(2,24)).toString(16)}`)

接下来在浏览器控制看看：something magic happens

具体分析请参见这篇文章：从一行代码里面学点JavaScript

6、论如何优雅的取随机字符串

Math.random().toString(16).substring(2)

Math.random().toString(36).substring(2)

7、(10)["toString"]() === "10"

解析请移步：js奇淫技巧1

8、匿名函数自执行

这么多写法你选择哪一种？我选择死亡。

( function() {}() );

( function() {} )();

[ function() {}() ];

~ function() {}();

! function() {}();

+ function() {}();

- function() {}();

delete function() {}();

typeof function() {}();

void function() {}();

new function() {}();

new function() {};

var f = function() {}();

1, function() {}();

1 ^ function() {}();

1 > function() {}();

// ...

9、另外一种undefined

从来不需要声明一个变量的值是undefined，因为JavaScript会自动把一个未赋值的变量置为undefined。所有如果你在代码里这么写，会被鄙视的

var data = undefined;

但是如果你就是强迫症发作，一定要再声明一个暂时没有值的变量的时候赋上一个undefined。那你可以考虑这么做：

 var data = void 0; // undefined

void在JavaScript中是一个操作符，对传入的操作不执行并且返回undefined。void后面可以跟()来用，例如void(0)，看起来是不是很熟悉？没错，在HTML里阻止带href的默认点击操作时，都喜欢把href写成javascript:void(0)，实际上也是依靠void操作不执行的意思。

当然，除了出于装逼的原因外，实际用途上不太赞成使用void，因为void的出现是为了兼容早起ECMAScript标准中没有undefined属性。void 0的写法让代码晦涩难懂。

10、论如何优雅的取整

var a = ~~2.33

var b= 2.33 | 0

var c= 2.33 >> 0

11、如何优雅的实现金钱格式化：1234567890 --> 1,234,567,890

用正则魔法实现：

var test1 = '1234567890'

var format = test1.replace(/\B(?=(\d{3})+(?!\d))/g, ',')

console.log(format) // 1,234,567,890

非正则的优雅实现：

 function formatCash(str) {

       return str.split('').reverse().reduce((prev, next, index) => {

            return ((index % 3) ? next : (next + ',')) + prev

       })

}

console.log(formatCash('1234567890')) // 1,234,567,890

12、这个我服，还有这个你很机智

我服

while (1) {

    alert('牛逼你把我关了啊')

}

你很机智，好一个障眼法

清除缓存： <a href="javascript:alert('清除成功');">清除缓存</a>

13、逗号运算符

var a = 0;

var b = ( a++, 99 );

console.log(a);  // 1

console.log(b);  // 99

14、论如何最佳的让两个整数交换数值

常规办法：

var a=1,b=2;

a += b;

b = a - b;

a -= b;

缺点也很明显，整型数据溢出，对于32位字符最大表示数字是2147483647，如果是2147483645和2147483646交换就失败了。
黑科技办法：

a ^= b;

b ^= a;

a ^= b;

哈哈，看不懂的童鞋建议去补习一下C语言的位操作，我就不去复习了，以前学嵌入式时候学的位操作都忘了

15、实现标准JSON的深拷贝

var a = {

    a: 1,

    b: { c: 1, d: 2 }

}

var b=JSON.parse(JSON.stringify(a))

不考虑IE的情况下，标准JSON格式的对象蛮实用，不过对于undefined和function的会忽略掉。

16、不用Number、parseInt和parseFloat和方法把"1"字符串转换成数字

哈哈，不准用强制类型转换，那么就想到了强大了隐式转换

var a =1

+a

17、如何装逼的写出"hello world!"

滚动条很长哦

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居然能运行，牛逼的隐式转换

18、parseInt(0.0000008) === 8

19、++[[]][+[]]+[+[]] == 10

强大的隐式转换，23333

20、0.1 + 0.2 == 0.3

0.1 +0.2 == 0.3 竟然是不成立的。。。。所以这就是为什么数据库存储对于货币的最小单位都是分。

简单说，0.1和0.2的二进制浮点表示都不是精确的，所以相加后不是0.3，接近（不等于）
0.30000000000000004。

所以，比较数字时，应该有个宽容值。ES6中这个宽容值被预定义了：Number.EPSILON。

21、最短的代码实现数组去重

[...new Set([1, "1", 2, 1, 1, 3])]

前不久面试阿里就问了这道题，哈哈，所以也写上一下

22、用最短的代码实现一个长度为m(6)且值都n(8)的数组

Array(6).fill(8)

这个够短了吧，好像是当初哪里看到的一个面试题，就自己想到了ES6的一些API

23、短路表达式

条件判断

var a = b && 1

    // 相当于

if (b) {

    a = 1

} else {

    a = b

}

var a = b || 1

    // 相当于

if (b) {

    a = b

} else {

    a = 1

}

24、JavaScript版迷宫

逃出迷宫，2333

25、取出一个数组中的最大值和最小值

var numbers = [5, 458 , 120 , -215 , 228 , 400 , 122205, -85411];

var maxInNumbers = Math.max.apply(Math, numbers);

var minInNumbers = Math.min.apply(Math, numbers);

26、将argruments对象转换成数组

var argArray = Array.prototype.slice.call(arguments);

或者ES6：

var argArray = Array.from(arguments)

27、javascript高逼格之Function构造函数

很多JavaScript教程都告诉我们，不要直接用内置对象的构造函数来创建基本变量，例如var arr = new Array(2); 的写法就应该用var arr = [1, 2];的写法来取代。

但是，Function构造函数（注意是大写的Function）有点特别。Function构造函数接受的参数中，第一个是要传入的参数名，第二个是函数内的代码（用字符串来表示）。

var f = new Function('a', 'alert(a)');

f('jawil'); // 将会弹出窗口显示jawil

这种方式可以根据传入字符串内容来创建一个函数是不是高大上？！

28、从一个数组中找到一个数，O(n)的算法，找不到就返回 null。

正常的版本:

function find (x, y) {

  for ( let i = 0; i < x.length; i++ ) {

    if ( x[i] == y ) return i;

  }

  return null;

}

let arr = [0,1,2,3,4,5]

console.log(find(arr, 2))

console.log(find(arr, 8))

结果到了函数式成了下面这个样子（好像上面的那些代码在下面若影若现，不过又有点不太一样，为了消掉if语言，让其看上去更像一个表达式，动用了 ? 号表达式）：

//函数式的版本

const find = ( f => f(f) ) ( f =>

  (next => (x, y, i = 0) =>

    ( i >= x.length) ?  null :

      ( x[i] == y ) ? i :

        next(x, y, i+1))((...args) =>

          (f(f))(...args)))

let arr = [0,1,2,3,4,5]

console.log(find(arr, 2))

console.log(find(arr, 8))