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仅用六个字符来完成Hello World，你能做到吗？
source link: http://blog.didispace.com/javascript-6-char-hello-world/
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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：
挑战：仅用六个字符来编写JavaScripte
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"
提取字母： ![] 可以获取 false ， ![] + [] 那可以获取 "false" 字符串，那么我们就可以通过下标获取其中的字母，比如： (![] + [])[1] 可以获取 false 字符串中第二位的字母 a
提取数字： ![] 可以获取 false ，由于 +false 可以获取 0 ，所以 +![] 就可以获取到 0 ；由于 +true 可以获取 1 ，所以 +!![] 就可以获取到 1 。这样依靠运算就可以获取更多其他数字
好了，有了这些基础基础知识之后，对于这个神奇的答案知道是怎么来的了吧？
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