.concat()连接后为什么把数组变成了string类型？

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.concat()连接后为什么把数组变成了string类型？Why does .concat() turn the array into a string type after concatenation?

I have defined two arrays, one is comment and the other is comment list Why does concat () become a string when splicing the commentlist? And the same is splicing. Why is comment an array type? I'm going to make a comment array and nest a comment list in it. I don't believe it

回答：

[userInfo.nickname].concat([userInfo.avatarUrl])