Question

  <script type="text/ecmascript">
  <![CDATA[
  function setCoordinates(circle) {
  var centerX = Math.round(Math.random() * 1000);
  var centerY = Math.round(Math.random() * 1000);      
  circle.setAttribute("cx",centerX);
  circle.setAttribute("cy",centerY);
  }
  ]]>
  </script>


  <circle class="circles" cx="500" cy="500" r="25" fill="white" filter="url(#f1)" />
  <circle class="circles" cx="500" cy="500" r="25" fill="white" filter="url(#f1)" />
  <circle class="circles" cx="500" cy="500" r="25" fill="white" filter="url(#f1)" />
  <circle class="circles" cx="500" cy="500" r="25" fill="white" filter="url(#f1)" />
  <circle class="circles" cx="500" cy="500" r="25" fill="white" filter="url(#f1)" />


  <script type="text/ecmascript">
  <![CDATA[
  setCoordinates(document.getElementsByClassName("circles"));
  ]]>
  </script>

This simply has no effect. However, when I used “getElementByID” and assigned an ID to the circle, it worked fine. (Opera)

Answer 1

document.getElementsByClassName returns a collection of elements, so you need to iterate over the results:

var elements = document.getElementsByClassName('circles');

for (var i = 0; i < elements.length; i++) {
    var element = elements[i];

    setCoordinates(element);
}

Check your JS console if your code doesn’t work properly. You should see errors like Object has no method 'setAttribute'.