Returning Value from Functions

Question

I am trying to use the console to show what image is linked to the thumbnail. I keep getting this error: console error

Here is my code: Js Code

var DETAIL_IMAGE_SELECTOR = '[data-image-role="target"]';

var DETAIL_TITLE_SELECTOR = '[data-image-role="title"]';

var THUMBNAIL_LINK_SELECTOR = '[data-image-role="trigger"]';


function setDetails(imageUrl, titleText) {
  'use strict';
  var detailImage = document.querySelector(DETAIL_IMAGE_SELECTOR);
  detailImage.setAttribute('src', imageUrl);

  var detailTitle = document.querySelector(DETAIL_TITLE_SELECTOR);
  detailTitle.textContent = titleText;
}

function imageFromThumb (thumbnail) {
  'use strict';
  return thumbnail.getAttribute('data-image-url');
}