LiveChat - custom variable via button

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>LiveChat custom variables via button</title>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" type="text/css" href="https://cdn.livechat-static.com/design-system/styles.css">
  </head>
  <body>
    <h1>Hi there!</h1>

    <p>
     This is a test page, add a custom variable by clicking the button below.
    </p>

    <script type="text/javascript">

      window.__lc = window.__lc || {};
      window.__lc.license = 9720060;
      (function() {
        var lc = document.createElement('script'); lc.type = 'text/javascript'; lc.async = true;
        lc.src = ('https:' == document.location.protocol ? 'https://' : 'http://') + 'cdn.livechatinc.com/tracking.js';
        var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(lc, s);
      })();
    var custom_variables = [
      { name: "Greeting", value: "True" }
    ];
    </script>
    <noscript>
    <a href="https://www.livechatinc.com/chat-with/9720060/" rel="nofollow">Chat with us</a>,
    powered by <a href="https://www.livechatinc.com/?welcome" rel="noopener nofollow" target="_blank">LiveChat</a>
    </noscript>
    <!-- End of LiveChat code -->
    <button class="lc-btn lc-btn--primary" onclick="LC_API.update_custom_variables(custom_variables);">Click me to add a custom variable</button>
  </body>
</html>