Variables defined with let behave differently (v3.2.45)

[kakikubo]

Vue version

3.2.45

Link to minimal reproduction

sfc link

Steps to reproduce

Start vue (up to 3.2.44) with yarn dev and access it with a browser using the following sample code.

<script setup lang="ts">
import { ref } from "vue";
const now = new Date();
const nowStr = now.toLocaleTimeString();
let timeStr = nowStr;
const timeStrRef = ref(nowStr);
function changeTime(): void {
  const newTime = new Date();
  const newTimeStr = newTime.toLocaleTimeString();
  timeStr = newTimeStr;
  timeStrRef.value = newTimeStr;
}
setInterval(changeTime, 1000);
</script>

<template>
  <p>timeStr: {{ timeStr }}</p>
  <p>timeStr(ref): {{ timeStrRef }}</p>
</template>

What is expected?

• timeStr => timeStr is fixed at the time when the screen is opened in the browser
• timeStr(ref) => timeStr(ref) is updated every second since the screen was opened in the browser

What is actually happening?

When the previous code is executed in vue 3.2.45, the behavior of timeStr and timeStr(ref) is the same.

• timeStr => timeStr is updated every second since the screen was opened in the browser
• timeStr(ref) => timeStr(ref) is updated every second since the screen was opened in the browser

System Info

System:
    OS: macOS 12.6.2
    CPU: (10) arm64 Apple M1 Pro
    Memory: 114.20 MB / 32.00 GB
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 18.12.1 - ~/.asdf/installs/nodejs/18.12.1/bin/node
    Yarn: 1.22.19 - ~/brew/bin/yarn
    npm: 8.19.2 - ~/.asdf/plugins/nodejs/shims/npm
  Browsers:
    Chrome: 108.0.5359.124
    Safari: 16.2
  npmPackages:
    vue: 3.2.45 => 3.2.45

Any additional comments?

Is there a mistake in the way it is written? If so, I would like to know if you can help me.

note

I can only reproduce this event with Vue SFC PlayGround with the same behavior as 3.2.45. You can actually use the terminal to specify 3.2.44 or 3.2.45 in package.json and run rm yarn.lock && yarn install && yarn dev, etc. to confirm.

[LinusBorg]

When the component re-renders because you changed the ref, the whole template is updated with all of the latest data. That's how re-renders work. the whole component template virtualDOM is re-rendered with the current data and diffed against the previous version.

[mpg-teruo-kakikubo]

@LinusBorg
Thank you.
Why is the behavior different from versions up to 3.2.44?

[LinusBorg]

It isn't - you an see for yourself in the playground, you can switch versions there. If you have a repository to share where this happens, please share it.

[kakikubo]

@LinusBorg

I have prepared a repository to reproduce this issue. We would appreciate it if you could check it here.
Thank you very much.
https://github.com/kakikubo/vuejs-core-issue-7417

[LinusBorg]

Ah ses, this was a bug that was fixed in 3.2.45. See:
#5655 (commit f73925d)