fix dragging feature of slide toc

src/components/slide-toc.vue

@@ -70,7 +70,7 @@
             </vue-final-modal>
         </div>
         <ul class="max-h-screen overflow-y-auto">
-            <draggable v-model="slides" @update="$emit('slides-updated', slides)" item-key="title" v-focus-list>
+            <draggable :list="slides" @update="$emit('slides-updated', slides)" :item-key="getSlideId" v-focus-list>
                 <template #item="{ element, index }">
                     <li
                         class="toc-slide border-t flex px-2 cursor-pointer hover:bg-gray-300"
@@ -324,6 +324,10 @@ export default class SlideTocV extends Vue {
         this.slides.splice(index + 1, 0, this.slides.splice(index, 1)[0]);
         this.$emit('slides-updated', this.slides);
     }
+
+    getSlideId(slide: Slide): string {
+        return slide.title + this.slides.indexOf(slide);
+    }
 }
 </script>