separated file into upload and download files, changed single quotes to double quotes, added progress indicator

public/download.js

@@ -0,0 +1,96 @@
+function download() {
+
+  var xhr = new XMLHttpRequest();
+  xhr.open("get", "/assets" + location.pathname.slice(0, -1), true);
+  xhr.responseType = "blob";
+
+  xhr.addEventListener("progress", updateProgress);
+
+  xhr.onload = function(e) {
+    if (this.status == 200) {
+      let self = this;
+      var blob = new Blob([this.response]);
+      var arrayBuffer;
+      var fileReader = new FileReader();
+      fileReader.onload = function() {
+        arrayBuffer = this.result;
+        var array = new Uint8Array(arrayBuffer);
+        salt = strToIv(location.pathname.slice(10, -1));
+
+        window.crypto.subtle.importKey(
+          "jwk",
+          {
+              kty: "oct",
+              k: location.hash.slice(1),
+              alg: "A128CBC",
+              ext: true,
+          },
+          {
+              name: "AES-CBC",
+          },
+          true,
+          ["encrypt", "decrypt"])
+        .then(function(key){  
+            window.crypto.subtle.decrypt(
+                {
+                    name: "AES-CBC",
+                    iv: salt,
+                },
+                key,
+                array)
+            .then(function(decrypted){
+                var dataView = new DataView(decrypted);
+                var blob = new Blob([dataView]);
+                var downloadUrl = URL.createObjectURL(blob);
+                var a = document.createElement("a");
+                a.href = downloadUrl;
+                a.download = xhr.getResponseHeader("Content-Disposition").match(/filename="(.+)"/)[1];
+                console.log(xhr.getResponseHeader("Content-Disposition"));
+                document.body.appendChild(a);
+                a.click();
+            })
+            .catch(function(err){
+                alert("This link is either invalid or has expired.");
+                console.error(err);
+            });
+        })
+        .catch(function(err){
+            console.error(err);
+        });
+      };
+      fileReader.readAsArrayBuffer(blob);
+    } else {
+      alert("Unable to download excel.")
+    }
+  };
+  xhr.send();
+}
+
+function ivToStr(iv) {
+  let hexStr = "";
+  for (var i in iv) {
+    if (iv[i] < 16) {
+      hexStr += "0" + iv[i].toString(16);
+    } else {
+      hexStr += iv[i].toString(16);
+    }
+  }
+  window.hexStr = hexStr;
+  return hexStr;
+}
+
+function strToIv(str) {
+  var iv = new Uint8Array(16);
+  for (var i = 0; i < str.length; i += 2) {
+    iv[i/2] = parseInt((str.charAt(i) + str.charAt(i + 1)), 16);
+  }
+
+  return iv;
+}
+
+function updateProgress(e) {
+  if (e.lengthComputable) { 
+    var percentComplete = Math.floor((e.loaded / e.total) * 100);
+    document.getElementById("downloadProgress").innerHTML = "Progress: " + percentComplete + "%";
+  } 
+}