title: javascript function running without being called
body: <p>I wonder why, as soon as the page loads, the function <code>btw_bijtellen ()</code> is called. I wanted to call it by clicking...</p>
  
  <pre><code>var $ = function (id) {
      return document.getElementById (id);
  }
  
  function btw_bijtellen () {
      window.alert("we want to calculate something after clicking th button");
  }
  
  $("bereken").onclick = btw_bijtellen ();
  </code></pre>