如何在Discord Bot的awaitMessages方法中使用多个过滤器？

SyntaxError: Identifier 'filter' has already been declared

这个错误是因为const声明的变量不允许在同一个块级作用域内重复定义。你当前使用的switch语句中，所有case默认处于同一作用域，在case0中声明的filter变量会作用于整个switch块，后续case再声明同名filter就会触发报错。

最优方案是给每个case添加独立的块级作用域，用大括号{}包裹每个case内的全部代码，这样每个case内声明的变量仅在当前case块内生效，不会和其他case的同名变量冲突，修改后的代码示例如下：

switch (yourCaseVariable) {
  case 0: { // 开启case0的独立作用域
    const LGEmbed0 = new Discord.MessageEmbed()
      .setTitle("Guess the Level!")
      .setDescription("Difficulty: Medium")
      .setColor("#36ff69")
      .setImage(
        "https://media.discordapp.net/attachments/891672414361112616/892153208082923520/fever.PNG"
      )
      .setFooter(
        `Requested by ${message.author.username}`,
        `https://cdn.discordapp.com/avatars/${message.author.id}/${message.author.avatar}.webp`
      )
      .setTimestamp();
    console.log("Answer: Fever");
    message.channel.send({
      embeds: [LGEmbed0],
    });

    const filter = (m) => m.content.startsWith("Fever");

    message.channel
      .awaitMessages({ filter, max: 1, time: 10000, errors: ["time"] })
      .then((collected) => message.channel.send({ embeds: [cor] }))
      .catch((collected) => message.channel.send({ embeds: [time] }));

    break;
  } // 闭合case0的独立作用域

  case 1: { // 开启case1的独立作用域
    const LGEmbed1 = new Discord.MessageEmbed()
      .setTitle("Guess the Level!")
      .setDescription("Difficulty: Harder")
      .setColor("#ff7d36")
      .setImage(
        "https://cdn.discordapp.com/attachments/891672414361112616/892153203465027685/beautiful_vacations.PNG"
      )
      .setFooter(`Requested by ${message.author.username}`)
      .setTimestamp();
    console.log("Answer: Beautiful Vacations");
    message.channel.send({
      embeds: [LGEmbed1],
    });

    // 可正常声明同名filter，不会和case0的变量冲突
    const filter = (m) => m.content.startsWith("Beautiful Vacations");
    message.channel
      .awaitMessages({ filter, max: 1, time: 10000, errors: ["time"] })
      .then((collected) => message.channel.send({ embeds: [cor] }))
      .catch((collected) => message.channel.send({ embeds: [time] }));
    break;
  }
}

也可以选择给不同case的filter变量起不同名称（比如filter0、filter1），但这种方案代码冗余度更高，不如独立作用域方案简洁。

内容的提问来源于stack exchange，提问作者KontrollFreek