javascript - 如何在继续代码之前捕获错误？

Question

我有一个命令可以向公会中的每个用户发送一条消息。当然，用户可能会关闭 DM。我想通过使用 .catch 来计算这些用户(并向 channel 发送一条消息，其中包含禁用它的用户数量)。

我的问题是，.catch block 在命令的其余部分之后 执行自身(向 channel 发送消息的部分) 在 .catch block 中，我将 1 添加到一个变量，每次它都会给我错误。 在 channel 消息中，我发送了变量。显然，该变量将为 0，因为它会在运行 .catch block 之前发送消息。

如何在.catch block 后发送消息以及关闭它的用户数量？

这是我的代码:

var text = args.join(' ')
message.guild.members.forEach(member => {
     member.send(text).catch(() => {
          console.log("Can't send DM to this user!")
          faultyusers++
     });
});
console.log(faultyusers);
message.channel.send("Successfully sent message to all members in the server. (Warning: **" + faultyusers + "** users might have not received the message because of their settings.)")

(当我运行此程序时，faultyusers 始终为 0。)

Answer 1

每个 member.send() 都是异步的。所以为此你需要创建一个 Promise对于每个 member.send() 调用。之后，你运行所有的 promise ，当它们全部解决时，你会得到一组结果，你可以从中计算没有收到消息的用户数量

// this function returns promise that will
// resolve with { success: true } or { success: false }
// depending on whether or not the user received the message (member.send() failed)
const sendMessageAndGetResult = (text, member) =>
    member
      .send(text)
      .then(() => ({ success: true }))
      .catch(() => ({ success: false }))

const sendMessages = async (text) => {
  // create one such promise for each user in guild
  const promises = message.guild.members.map(member => sendMessageAndGetResult(text, member))
  // wait until all promises are resolved
  // allResults will be an looking like this [{ success: true }, { success: false }, ...]
  const allResults = await Promise.all(promises)
  // count users that did not receive message
  const faultyUsersCount = allResults.filter(result => !result.success).length
  console.log(faultyUsersCount)
  message.channel.send("Successfully sent message to all members in the server. (Warning: **" + faultyUsersCount + "** users might have not received the message because of their settings.)")
}

// usage
sendMessages('hello')