为什么alert（[“a”，“b”，“c”，“d”，“e”] [[1,2]，3,4]）在javascript中输出e？

Question

有人能告诉我为什么：

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

在JavaScript而输出E？

Answer 1

因为逗号是执行所有分离指令的运算符（in fact：两条指令，每条指令也可以使用逗号运算符）并返回最后一条指令的结果。 I.e .:

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