getElementsByClassName

HTML

<html>
  <head></head>
  <body>
    <div id="this-id">Essa <code>div</code> será selecionada pelo <code>id</code></div>
    <div class="class-name">Essa <code>div</code> será selecionada pelo nome da <code>class</code></div>
  </body>
</html>

JavaScript

var url = document.getElementById('this-id').textContent
alert(url);

var url = document.getElementsByClassName('class-name')[0].textContent
alert(url);