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diff --git a/src/static/js/xhr-util.js b/src/static/js/xhr-util.js
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+/* eslint-env browser */
+
+/**
+ * This fetch function is adapted from a `loadImage` function
+ * credited to Parziphal, Feb 13, 2017.
+ * https://stackoverflow.com/a/42196770
+ *
+ * The callback is generally run with the loading progress as a decimal 0-1.
+ * However, if it's not possible to compute the progress ration (which might
+ * only become apparent after a progress amount *has* been sent!),
+ * the callback will be run with the value -1.
+ *
+ * The return promise resolves to a manually instantiated Response object
+ * which generally behaves the same as a normal fetch response; access headers,
+ * text, blob, arrayBuffer as usual. Accordingly, non-200 responses do *not*
+ * reject the prmoise, so be sure to check the response status yourself.
+ */
+export function fetchWithProgress(url, progressCallback) {
+  return new Promise(resolve => {
+    const xhr = new XMLHttpRequest();
+    let notifiedNotComputable = false;
+
+    xhr.open('GET', url, true);
+    xhr.responseType = 'arraybuffer';
+
+    xhr.onprogress = event => {
+      if (notifiedNotComputable) {
+        return;
+      }
+
+      if (!event.lengthComputable) {
+        notifiedNotComputable = true;
+        progressCallback(-1);
+        return;
+      }
+
+      progressCallback(event.loaded / event.total);
+    };
+
+    xhr.onloadend = () => {
+      const body = xhr.response;
+
+      const options = {
+        status: xhr.status,
+        headers:
+          parseResponseHeaders(xhr.getAllResponseHeaders()),
+      };
+
+      resolve(new Response(body, options));
+    };
+
+    xhr.send();
+  });
+
+  function parseResponseHeaders(headers) {
+    return (
+      Object.fromEntries(
+        headers
+          .trim()
+          .split(/[\r\n]+/)
+          .map(line => line.match(/(.+?):\s*(.+)/))
+          .map(match => [match[1], match[2]])));
+  }
+}