Hello World 对于每一个开发者来说都不陌生，因为在我们学习任何一个语言或框架的时候，都会有一个Hello World的案例来帮助我们快速入门。
如果我们使用JavaScript来输出Hello World的话，可以这样写：
alert("Hello World");放入HTML：
<html> <script type="text/javascript"> alert("Hello World"); </script> </html>在浏览器中打开就可以如下情况输出Hello World了：
上面我们在JavaScript中实现Hello World的时候，除去HTML相关的标签和属性，上面的实现语句alert("Hello World");一共使用了13个字符，那么有没有办法用更少的字符来实现一样的功能呢？今天我们就来挑战一下：有没有办法仅使用6个字符来编写JavaScripte程序，以实现Hello World的输出？
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先思考一下，有思路没？没思路的话，下面有提示...
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提示：使用这六个字符：(，)，+，[，]，!
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再思考一下，有思路没？没思路的话，下面有答案和解析...
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答案：
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</script> </html>什么？你不信这可以输出Hello World？那么你可以将其复制下来，放到HTML文件中，再打开试试吧！
为什么？为什么我们可以仅使用这6个字符来编写这些奇奇怪怪的JavaScript代码？这完全是由于JavaScript独特的类型系统和转换机制。
上面的6个字符可以分为三类：
[，]：用于创建数组
!，+：对数组执行一些操作
(，)：对操作进行分组
基础原理
[]可以用来创建数组，而![]则可以返回false
预定义的规则：2 + true，会转化为2 + 1，最后得到3
预定义的规则：2 + "2"，会转化为2 + "2"，最后得到"22"