首先，看如下JavaScript代码

　　看到这里，你是否眼花缭乱，没有头绪呢?只用 []()!+ 这六个字符就可以实现一段可执行的 JavaScipt 代码，这是如何实现的呢?

　　类型转换

　　JavaScript 是弱类型的编程语言，我们在写代码的时候充斥着大量的类型转换，如下表

　　根据数据类型转换：

　　· !后的字符会被转换为布尔值

　　//false

　　![]

　　//true

　　!![]

　　//undefined

　　[][[]]

　　//NaN

　　+[![]]

　　· +后的字符会被转换为数值

　　//结果是什么呢?提示：[]被转换为0

　　+[] === 0

　　//结果是什么呢?提示：[]被转换为0,!0是true,+true是1

　　+!+[] === 1

　　//结果是什么呢?

　　[+!+[]] + [+[]]] === [1]+[0] === '10'

　　· +[] 前的字符会被转换为字符串

　　//结果是什么呢?

　　!+[]+!+[] === 2

　　思考1

　　//1.提示：+[]被转换为0，[][0]为undefined

　　[][ +[] ] === undefined

　　//2.提示：false +[]为'false',[+!![]]为1，所以结果为a——扩展后可以获取到想要的字母

　　(false +[]) [+!![]] === 'a'

　　//3.提示：0["constructor"]为Number,Number+[]转为字符串"function Number(){}"

　　0["constructor"]+[]

　　//4.提示：通过 []["find"] 可以拿到数组的 find 方法，find 方法的构造函数其实就是 Function

　　[]["find"]["constructor"] === Function

　　思考2

　　根据以上内容推导：

　　//1.表示f

　　(![]+[])[+[]]

　　//2.表示find

　　(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+([][[]]+[])[!+[]+!+[]]

　　//3.表示constructor

　　([][(![]+[])[+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]]+(!![]+[])[+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[][(![]+[])[+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]]+(!![]+[])[+[]]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+[]]+([][(![]+[])[+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]]+(!![]+[])[+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[][(![]+[])[+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]]+(!![]+[])[+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]

　　//4.表示alert

　　(![]+[])[+!+[]]+(![]+[])[!+[]+!+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]+(!![]+[])[+[]]

　　//5.表示 []["find"]["constructor"]("alert(1)")()：

　　[][(![]+[])[+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]]+(!![]+[])[+[]]][([][(![]+[])[+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]]+(!![]+[])[+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[][(![]+[])[+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]]+(!![]+[])[+[]]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+[]]+([][(![]+[])[+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]]+(!![]+[])[+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[][(![]+[])[+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]]+(!![]+[])[+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]]((![]+[])[+!+[]]+(![]+[])[!+[]+!+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]+(!![]+[])[+[]]+([][(![]+[])[+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]]+(!![]+[])[+[]]]+[])[+!+[]+[!+[]+!+[]+!+[]]]+[+!+[]]+([+[]]+![]+[][(![]+[])[+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[+!+[]]+(!![]+[])[+[]]])[!+[]+!+[]+[+[]]])()

　　你明白了吗?