title: Discordbot javascript react to mentions
body: <p>I'm completely new to Javascript and i would like to make a discord bot. 
  I have a bot already running with a few commands, now i would like to add something that posts a reaction whenever someone specific is tagged. </p>
  
  <pre><code>client.on('message', message =&gt; {
    var user = "123456479879541";
    if(message.mentions.users.id === user) {
      message.channel.send('ok');
    }
  });
  </code></pre>
  
  <p>What do i have to do to make it work?</p>