Make oldVNode monomorphic

src/constants.js

@@ -1,3 +1,5 @@
+import { createVNode } from './create-element';
+
 /** Normal hydration that attaches to a DOM tree but does not diff it. */
 export const MODE_HYDRATE = 1 << 5;
 /** Signifies this VNode suspended on the previous render */
@@ -12,5 +14,7 @@ export const RESET_MODE = ~(MODE_HYDRATE | MODE_SUSPENDED);
 
 export const EMPTY_OBJ = /** @type {any} */ ({});
 export const EMPTY_ARR = [];
+export const EMPTY_VNODE = createVNode(null, EMPTY_OBJ, null, null);
+// EMPTY_VNODE._children = []
 export const IS_NON_DIMENSIONAL =
 	/acit|ex(?:s|g|n|p|$)|rph|grid|ows|mnc|ntw|ine[ch]|zoo|^ord|itera/i;

src/diff/children.js

@@ -1,6 +1,6 @@
 import { diff, unmount, applyRef } from './index';
 import { createVNode, Fragment } from '../create-element';
-import { EMPTY_OBJ, EMPTY_ARR, INSERT_VNODE, MATCHED } from '../constants';
+import { EMPTY_ARR, INSERT_VNODE, MATCHED, EMPTY_VNODE } from '../constants';
 import { isArray } from '../util';
 import { getDomSibling } from '../component';
 
@@ -67,9 +67,9 @@ export function diffChildren(
 		// At this point, constructNewChildrenArray has assigned _index to be the
 		// matchingIndex for this VNode's oldVNode (or -1 if there is no oldVNode).
 		if (childVNode._index === -1) {
-			oldVNode = EMPTY_OBJ;
+			oldVNode = EMPTY_VNODE;
 		} else {
-			oldVNode = oldChildren[childVNode._index] || EMPTY_OBJ;
+			oldVNode = oldChildren[childVNode._index] || EMPTY_VNODE;
 		}
 
 		// Update childVNode._index to its final index

src/render.js

@@ -1,4 +1,4 @@
-import { EMPTY_OBJ } from './constants';
+import { EMPTY_OBJ, EMPTY_VNODE } from './constants';
 import { commitRoot, diff } from './diff/index';
 import { createElement, Fragment } from './create-element';
 import options from './options';
@@ -39,7 +39,7 @@ export function render(vnode, parentDom, replaceNode) {
 		// Determine the new vnode tree and store it on the DOM element on
 		// our custom `_children` property.
 		vnode,
-		oldVNode || EMPTY_OBJ,
+		oldVNode || EMPTY_VNODE,
 		EMPTY_OBJ,
 		parentDom.namespaceURI,
 		!isHydrating && replaceNode