这个问题在这里已有答案：

• JavaScript property access: dot notation vs. brackets? 12个答案

使用括号内的变量。

const package = {
  "servers": {
    "folder1": {
      "modrole": "Moderator"
    },
    "folder2": {
      "modrole": "bot owner"
    }
  }
}
let folderName = "folder1"
console.log(package.servers[folderName].modrole)

有没有办法在另一个变量的路径中包含变量？ [重复]

const package = {
  "servers": {
    "folder1": {
      "modrole": "Moderator"
    },
    "folder2": {
      "modrole": "bot owner"
    }
  }
}
let folderName = "folder1"
console.log(package.servers[folderName].modrole)