Simplify delay behaviour, add JSDoc comments

client/src/utils/download.js

@@ -1,32 +1,42 @@
-// adapted from https://github.com/sindresorhus/multi-download/blob/v4.0.0/index.js
+// Adapted from https://github.com/sindresorhus/multi-download/blob/v4.0.0/index.js
 // to take File as input https://developer.mozilla.org/en-US/docs/Web/API/File
-const delay = milliseconds => new Promise(resolve => {
-  setTimeout(resolve, milliseconds);
-});
 
-const download = async (file) => {
+/**
+ * Creates a promise that resolves after the specified number of milliseconds
+ */
+const delay = (milliseconds: number): Promise<void> => {
+  return new Promise((resolve) => setTimeout(resolve, milliseconds));
+};
+
+/**
+ * Downloads a single file
+ * @param file - An instance of the File type representing the file to download
+ */
+const download = async (file: File): Promise<void> => {
   const a = document.createElement('a');
   const url = URL.createObjectURL(file);
   a.download = file.name;
   a.href = url;
   a.style.display = 'none';
-  document.body.append(a);
+  document.body.appendChild(a);
   a.click();
-
-  // Chrome requires the timeout
-  await delay(100);
+  await delay(100); // Needed for Chrome
   a.remove();
-
   URL.revokeObjectURL(url);
 };
 
-const multiDownload = async (files) => {
+/**
+ * Initiates multiple file downloads with a delay between each one
+ * @param files - An array of instances of the File type representing the files to download
+ */
+const multiDownload = async (files: readonly File[]): Promise<void> => {
   if (!files) {
     throw new Error('`files` required');
   }
-
-  for (const [index, file] of files.entries()) {
-    await delay(index * 1000); // eslint-disable-line no-await-in-loop
+
+  // Trigger a download every second
+  for (const file of files) {
+    await delay(1000);
     download(file);
   }
-}
+};