Added beforeClose option to modals

We have unsaved changes confirmation modals that open when a close of another modal (typically attached to a route) is attempted. When that occurs we want to stop the original modal from closing until the confirmation modal promise is complete.

- when `closeModal()` is called, check if `beforeClose()` was passed in as an option, if it was then call it and await the result, if the result is `false` then the close is cancelled

README.md

@@ -4,3 +4,4 @@ Not recommended for general use, this package will be removed if upstream become
 
 Custom changes:
 - added `.finally()` to modal instances so the Promise-like interface is more complete. Useful for cleanup after a modal is resolved/rejected without duplication
+- added `beforeClose()` as an option that can be passed when opening a modal, if the function returns `false` then the modal close will be aborted

addon/components/modal.js

@@ -95,7 +95,14 @@ export default Component.extend({
     this._super(...arguments);
   },
 
-  closeModal(result) {
+  async closeModal(result) {
+    if (this.modal._options.beforeClose) {
+      let allowClose = await this.modal._options.beforeClose(result);
+      if (allowClose === false) {
+        return;
+      }
+    }
+
     // Trigger out animation
     set(this, 'animatingOutClass', this.outAnimationClass);