爲什麼alert（[「a」，「b」，「c」，「d」，「e」] [[1,2]，3,4]）在javascript中輸出e？

Question

有人能告訴我爲什麼：

alert(["a","b","c","d","e"][[1,2],3,4]) 

在JavaScript而輸出E？

Answer 1

因爲逗號是執行所有分離指令的運算符（in fact：兩條指令，每條指令也可以使用逗號運算符）並返回最後一條指令的結果。 I.e .:

["a","b","c","d","e"][[1,2],3,4] => ["a","b","c","d","e"][4] === "e"