feat: add slot-listener for dropdown and others

src/utils/getFirstSlotNode.ts

@@ -0,0 +1,24 @@
+import type { Slots, VNode } from 'vue'
+import { flatten } from './flatten'
+
+// ref: https://github.com/TuSimple/naive-ui/blob/main/src/popover/src/Popover.tsx
+
+export function getFirstSlotVNode (
+    slots: Slots,
+    slotName = 'default',
+    props: unknown = undefined,
+): VNode | null {
+    const slot = slots[slotName]
+    if (!slot) {
+        console.warn('getFirstSlotVNode', `slot[${slotName}] is empty`)
+        return null
+    }
+    const slotContent = flatten(slot(props))
+    // vue will normalize the slot, so slot must be an array
+    if (slotContent.length === 1) {
+        return slotContent[0]
+    } else {
+        console.warn('getFirstSlotVNode', `slot[${slotName}] should have exactly one child`)
+        return null
+    }
+}