title: Return the channel ID of a channel mentioned in a command
body: <p>The title says all. I'm making a Discord bot in node.js, and one part that I'm trying to add is a <code>.setup</code> command, to make the bot less dependent on manually changing the value of <code>client.channels.get().send()</code>, allowing it to be more easily set up in the future. </p>
  
  <p>Anyway, in my case, I'm trying to have the user reply to a message with a channel mention (like #welcome for example), and have the bot return that ID and save it to a variable. </p>
  
  <p>Currently, I have this:</p>
  
  <pre class="lang-js prettyprint-override"><code>function setupChannel() {
    client.channels.get(setupChannelID).send('Alright. What channel would you like me to send my reminders to?');
    client.on('message', message =&gt; {
      checkChannel = message.mentions.channels.first().id;
      client.channels.get(setupChannelID).send('Ok. I\'ll send my reminders to that channel.');
    });
  }
  </code></pre>
  
  <p><code>message.mentions.channels</code> returns undefined.<br>
  I know that the <code>message.mentions.channels.first().id</code> bit works when its a user instead of a channel, is there a different way of getting a channel mention in a message? </p>