Improve async/await usage, and sort init calls in index.js (#17386)

* clean up async/await, and sort init calls in `index.js
* use `const _promise` to indicate that we do not need await an async function

web_src/js/features/repo-migration.js

@@ -0,0 +1,60 @@
+const $service = $('#service_type');
+const $user = $('#auth_username');
+const $pass = $('#auth_password');
+const $token = $('#auth_token');
+const $mirror = $('#mirror');
+const $lfs = $('#lfs');
+const $lfsSettings = $('#lfs_settings');
+const $lfsEndpoint = $('#lfs_endpoint');
+const $items = $('#migrate_items').find('input[type=checkbox]');
+
+export default function initRepoMigration() {
+  checkAuth();
+  setLFSSettingsVisibility();
+
+  $user.on('keyup', () => {checkItems(false)});
+  $pass.on('keyup', () => {checkItems(false)});
+  $token.on('keyup', () => {checkItems(true)});
+  $mirror.on('change', () => {checkItems(true)});
+  $('#lfs_settings_show').on('click', () => { $lfsEndpoint.show(); return false });
+  $lfs.on('change', setLFSSettingsVisibility);
+
+  const $cloneAddr = $('#clone_addr');
+  $cloneAddr.on('change', () => {
+    const $repoName = $('#repo_name');
+    if ($cloneAddr.val().length > 0 && $repoName.val().length === 0) { // Only modify if repo_name input is blank
+      $repoName.val($cloneAddr.val().match(/^(.*\/)?((.+?)(\.git)?)$/)[3]);
+    }
+  });
+}
+
+function checkAuth() {
+  const serviceType = $service.val();
+
+  checkItems(serviceType !== 1);
+}
+
+function checkItems(tokenAuth) {
+  let enableItems;
+  if (tokenAuth) {
+    enableItems = $token.val() !== '';
+  } else {
+    enableItems = $user.val() !== '' || $pass.val() !== '';
+  }
+  if (enableItems && $service.val() > 1) {
+    if ($mirror.is(':checked')) {
+      $items.not('[name="wiki"]').attr('disabled', true);
+      $items.filter('[name="wiki"]').attr('disabled', false);
+      return;
+    }
+    $items.attr('disabled', false);
+  } else {
+    $items.attr('disabled', true);
+  }
+}
+
+function setLFSSettingsVisibility() {
+  const visible = $lfs.is(':checked');
+  $lfsSettings.toggle(visible);
+  $lfsEndpoint.hide();
+}