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　　首先，看如下JavaScript代碼

　　看到這里，你是否眼花繚亂，沒有頭緒呢?只用 []()!+ 這六個字符就可以實現一段可執行的 JavaScipt 代碼，這是如何實現的呢?

　　類型轉換

　　JavaScript 是弱類型的編程語言，我們在寫代碼的時候充斥著大量的類型轉換，如下表

　　根據數據類型轉換：

　　· !后的字符會被轉換為布爾值

　　//false

　　![]

　　//true

　　!![]

　　//undefined

　　[][[]]

　　//NaN

　　+[![]]

　　· +后的字符會被轉換為數值

　　//結果是什么呢?提示：[]被轉換為0

　　+[] === 0

　　//結果是什么呢?提示：[]被轉換為0,!0是true,+true是1

　　+!+[] === 1

　　//結果是什么呢?

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

　　· +[] 前的字符會被轉換為字符串

　　//結果是什么呢?

　　!+[]+!+[] === 2

　　思考1

　　//1.提示：+[]被轉換為0，[][0]為undefined

　　[][ +[] ] === undefined

　　//2.提示：false +[]為'false',[+!![]]為1，所以結果為a——擴展后可以獲取到想要的字母

　　(false +[]) [+!![]] === 'a'

　　//3.提示：0["constructor"]為Number,Number+[]轉為字符串"function Number(){}"

　　0["constructor"]+[]

　　//4.提示：通過 []["find"] 可以拿到數組的 find 方法，find 方法的構造函數其實就是 Function

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

　　思考2

　　根據以上內容推導：

　　//1.表示f

　　(![]+[])[+[]]

　　//2.表示find

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

　　//3.表示constructor

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

　　//4.表示alert

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

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

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

　　你明白了嗎?