https://heathermaeerickson.com/release/locke/production/v0.0.141/js/gallery.js

1(function (w, d) {
2  "use strict";
3
4  // Copy img src to rollover text box mask image on load, this is an easy way
5  // to lazyload the mask image and keep it in sync with the preview
6  // image. Because the load event will fire each time the image src changes,
7  // this ensures that they are both using the same src at all times.
8  d.addEventListener('lazybeforeunveil', function (e) {
9    var img = e.target;
10    var id = img.getAttribute('data-tb-mask-image-id');
11    !!id && img.addEventListener('load', function (e) {
12      var img = e.target; // avoid closing over img
13      var maskImage = d.getElementById(id);
14      if (maskImage) {
15        maskImage.setAttribute('href', img.currentSrc);
16        maskImage.setAttribute('xlink:href', img.currentSrc);
17      }
18    });
19  });
20
21}(window, document));