commit

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "svelte",
-  "version": "3.17.0",
+  "version": "3.17.1",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {

src/runtime/internal/transitions.ts

@@ -207,6 +207,12 @@ export function create_out_transition(node: Element & ElementCSSInlineStyle, fn:
 			config = config();
 			go();
 		});
+	} else if (config && config.then) {
+		add_render_callback(() => dispatch(node, false, 'start'));
+		config.then(() => {
+			dispatch(node, false, 'end');
+			if (!--group.r) run_all(group.c);
+		});
 	} else {
 		go();
 	}

src/runtime/transition/index.ts

@@ -4,6 +4,7 @@ import { assign, is_function } from 'svelte/internal';
 type EasingFunction = (t: number) => number;
 
 export interface TransitionConfig {
+	then?: Promise<any>['then'];
 	delay?: number;
 	duration?: number;
 	easing?: EasingFunction;