Fire event handler of input element in a dialog? [solved]

var infoTab = dialogDefinition.getContents('info');
var hboxElem = infoTab.elements[0].children[0];
hboxElem.children[1] = {   // replace 'browse' uiElement
  type : 'html',
  html : '<a href="#" onclick="window.open(\'<url to our image selector\');">Choose image...</a>',
  style : 'display: inline-block; margin-top: 10px;'
};

function selectImage(id, imgId) {
  var urlField = opener.document.getElementById('60_textInput');
  urlField.value = '<url of selected image>';
  urlField.onchange();   // <- this does not work
  window.close();   // close popup
}