这部分主要说两个方面,1是静态提升，2是事件监听缓存

静态提升意思就是说，在以往Vue执行函数的时候，无论是绑定数据的节点还是没有绑定的，都会在render函数执行的时候重新渲染,如下代码所示

import { createVNode as _createVNode, toDisplayString as _toDisplayString, openBlock as _openBlock, createBlock as _createBlock } from "vue"

export function render(_ctx, _cache, $props, $setup, $data, $options) {
  return (_openBlock(), _createBlock("div", null, [
    _createVNode("p", null, "HELLO WORLD"),
    _createVNode("div", null, _toDisplayString(_ctx.msg), 1 /* TEXT */)
  ]))
}

　做了静态提升之后，

import { createVNode as _createVNode, toDisplayString as _toDisplayString, openBlock as _openBlock, createBlock as _createBlock } from "vue"

const _hoisted_1 = /*#__PURE__*/_createVNode("p", null, "HELLO WORLD", -1 /* HOISTED */)

export function render(_ctx, _cache, $props, $setup, $data, $options) {
  return (_openBlock(), _createBlock("div", null, [
    _hoisted_1,
    _createVNode("div", null, _toDisplayString(_ctx.msg), 1 /* TEXT */)
  ]))
}

　静态的节点被提升到渲染函数外部，然后只会在首次的时候执行一下节点创建函数，以后每次渲染都拿外面的那个变量就完事了;

事件监听缓存

在以往的Vue版本中,事件是被当做一种动态属性来监听的,如下所示

import { createVNode as _createVNode, toDisplayString as _toDisplayString, openBlock as _openBlock, createBlock as _createBlock } from "vue"

const _hoisted_1 = /*#__PURE__*/_createVNode("p", null, "HELLO WORLD", -1 /* HOISTED */)

export function render(_ctx, _cache, $props, $setup, $data, $options) {
  return (_openBlock(), _createBlock("div", null, [
    _hoisted_1,
    _createVNode("div", null, _toDisplayString(_ctx.msg), 1 /* TEXT */),
    _createVNode("span", { onClick: _ctx.save }, null, 8 /* PROPS */, ["onClick"])
  ]))
}

_createVNode("span", { onClick: _ctx.save }, null, 8 /* PROPS */, ["onClick"]) 这部分就是绑定事件的节点,8代表动态属性,具体可参考上一篇;但是我们的事件监听函数，基本上是不会动态改变的；所以再进行监听是完全没有必要的，所以Vue3做了以下优化

import { createVNode as _createVNode, toDisplayString as _toDisplayString, openBlock as _openBlock, createBlock as _createBlock } from "vue"

const _hoisted_1 = /*#__PURE__*/_createVNode("p", null, "HELLO WORLD", -1 /* HOISTED */)

export function render(_ctx, _cache, $props, $setup, $data, $options) {
  return (_openBlock(), _createBlock("div", null, [
    _hoisted_1,
    _createVNode("div", null, _toDisplayString(_ctx.msg), 1 /* TEXT */),
    _createVNode("span", {
      onClick: _cache[1] || (_cache[1] = (...args) => (_ctx.save && _ctx.save(...args)))
    })
  ]))
}

onClick: _cache[1] || (_cache[1] = (...args) => (_ctx.save && _ctx.save(...args))) 由此可见，onClick:不再具有动态属性的标志,不是动态的，自然也不会生成监听了。效率自然也提高了;