title: Laravel echo send data when joining channel
body: <p>How do I receive data when the client initially joins a channel?</p>
  <p>Something like this:</p>
  <pre><code>Echo.channel('channel-name')
      .onjoin(function (data) {
          console.log(data) // Data received from server
      })
  </code></pre>
  <p>As soon when the client joins, the server should respond with data, preferably with PHP.</p>