Link: Click here for a button!

Display button here: 


Code:
  <a href="javascript:void(0);"
        onclick="renderYtSubscribeButton('GoogleDevelopers')">Click here for a button!</a>
  Display button here: <div id="yt-button-container-render"></div>
  <script>
    function renderYtSubscribeButton(channel) {
      var container = document.getElementById('yt-button-container-render');
      var options = {
        'channel': channel,
        'layout': 'full'
      };
      gapi.ytsubscribe.render(container, options);
    }
  </script>

  <b>Link:</b>
  <a href="javascript:void(0);"
        onclick="renderYtSubscribeButton('GoogleDevelopers')">Click here for a button!</a>

  <b>Display button here:</b>
  <div id="yt-button-container-render" style="display:inline"></div>