improve perf by reducing prop access (#3956)

Author: JoviDeCroock

src/diff/children.js

@@ -2,6 +2,7 @@ import { diff, unmount, applyRef } from './index';
 import { createVNode, Fragment } from '../create-element';
 import { EMPTY_OBJ, EMPTY_ARR } from '../constants';
 import { getDomSibling } from '../component';
+import { isArray } from '../util';
 
 /**
  * Diff the children of a virtual node
@@ -70,7 +71,7 @@ export function diffChildren(
 				null,
 				childVNode
 			);
-		} else if (Array.isArray(childVNode)) {
+		} else if (isArray(childVNode)) {
 			childVNode = newParentVNode._children[i] = createVNode(
 				Fragment,
 				{ children: childVNode },
@@ -265,7 +266,7 @@ function reorderChildren(childVNode, oldDom, parentDom) {
 export function toChildArray(children, out) {
 	out = out || [];
 	if (children == null || typeof children == 'boolean') {
-	} else if (Array.isArray(children)) {
+	} else if (isArray(children)) {
 		children.some(child => {
 			toChildArray(child, out);
 		});

src/diff/index.js

@@ -3,7 +3,7 @@ import { Component, getDomSibling } from '../component';
 import { Fragment } from '../create-element';
 import { diffChildren } from './children';
 import { diffProps, setProperty } from './props';
-import { assign, removeNode, slice } from '../util';
+import { assign, isArray, removeNode, slice } from '../util';
 import options from '../options';
 
 /**
@@ -232,7 +232,7 @@ export function diff(
 
 			diffChildren(
 				parentDom,
-				Array.isArray(renderResult) ? renderResult : [renderResult],
+				isArray(renderResult) ? renderResult : [renderResult],
 				newVNode,
 				oldVNode,
 				globalContext,
@@ -438,7 +438,7 @@ function diffElementNodes(
 			i = newVNode.props.children;
 			diffChildren(
 				dom,
-				Array.isArray(i) ? i : [i],
+				isArray(i) ? i : [i],
 				newVNode,
 				oldVNode,
 				globalContext,

src/util.js

@@ -1,5 +1,7 @@
 import { EMPTY_ARR } from './constants';
 
+export const isArray = Array.isArray;
+
 /**
  * Assign properties from `props` to `obj`
  * @template O, P The obj and props types