如何使Discord bot DM用户获得特定答复？

Question

I'm trying to make my bot having a DM commands that can send a specific user with a specific DM message.

For example:

Me: !dm @user#6969 hi who ru

Bot: Messages user#6969 "hello who ru"

Currently using Visual Studio Code to code the stuff, and I don't really know how do I make this command due to I couldn't really find a working tutorial about it.

if(message.content.startsWith(`${prefix}dm`)) {
    var mention = message.mentions.members.first()
    mention.send("hi")
}

Here's the error:

mention.send("hi")
         ^

TypeError: Cannot read property 'send' of undefined
    at Client.client.on.message (/Users/Private/Desktop/Discord/bot/index.js:69:17)
    at Client.emit (events.js:198:13)
    at MessageCreateHandler.handle (/Users/Private/Desktop/Discord/bot/node_modules/discord.js/src/client/websocket/packets/handlers/MessageCreate.js:9:34)
    at WebSocketPacketManager.handle (/Users/Private/Desktop/Discord/bot/node_modules/discord.js/src/client/websocket/packets/WebSocketPacketManager.js:105:65)
    at WebSocketConnection.onPacket (/Users/Private/Desktop/Discord/bot/node_modules/discord.js/src/client/websocket/WebSocketConnection.js:333:35)
    at WebSocketConnection.onMessage (/Users/Private/Desktop/Discord/bot/node_modules/discord.js/src/client/websocket/WebSocketConnection.js:296:17)
    at WebSocket.onMessage (/Users/Private/Desktop/Discord/bot/node_modules/ws/lib/event-target.js:120:16)
    at WebSocket.emit (events.js:198:13)
    at Receiver.receiverOnMessage (/Users/Private/Desktop/Discord/bot/node_modules/ws/lib/websocket.js:789:20)
    at Receiver.emit (events.js:198:13)```

Answer 1

if(message.content.startsWith(`${prefix}dm`)) {
    const mentionedUser = message.mentions.users.first();
    if(!mentionedUser) return message.reply('Mention Somebody');
    mentionedUser.send('Hi');
}