fix lint, add jsdoc

src/Modal.js

@@ -170,6 +170,12 @@ class ModalManager {
         }, deferred.promise];
     }
 
+    /**
+     * @callback onBeforeClose
+     * @param {string?} reason either "backgroundClick" or null
+     * @return {Promise<bool>} whether the dialog should close
+     */
+
     /**
      * Open a modal view.
      *
@@ -197,6 +203,8 @@ class ModalManager {
      *                                 also be removed from the stack. This is not compatible
      *                                 with being a priority modal. Only one modal can be
      *                                 static at a time.
+     * @param {Object} options? extra options for the dialog
+     * @param {onBeforeClose} options.onBeforeClose a callback to decide whether to close the dialog
      * @returns {object} Object with 'close' parameter being a function that will close the dialog
      */
     createDialogAsync(prom, props, className, isPriorityModal, isStaticModal, options = {}) {