refactor: use symbol for private properties

[Alfred-Skyblue]

I have seen many places where HTMLElement's properties are extended, such as the addition of the _assign property to the Element in vModel. Should we use Symbol properties for such extensions? This would prevent users from accessing and tampering with these properties.

[sxzz]

/ecosystem-ci run

[vue-bot]

📝 Ran ecosystem CI: Open

suite	result
nuxt	✅ success
pinia	✅ success
quasar	❌ failure
router	✅ success
test-utils	✅ success
vant	✅ success
vite-plugin-vue	✅ success
vitepress	✅ success
vue-i18n	✅ success
vue-macros	❌ failure
vuetify	✅ success
vueuse	✅ success
vue-simple-compiler	✅ success

[sxzz]

Thank you for your excellent work! However, I am concerned that using symbols as keys may incur greater performance overhead compared to strings. Can you attempt to test whether it will have a significant impact on performance? If so, we need to consider if this PR is truly worth it. If there is not much performance degradation, we believe your PR is valuable!

[Alfred-Skyblue]

Taking the example of running "set" 10, 100, and 1000 times, as the quantity increases, the performance difference between symbols and strings will become smaller. Of course, if we consider ten runs, symbols take 0.078ms, while strings take 0.015ms.

[sxzz]

https://jsben.ch/9mNDi

I have tested using both string keys and symbol keys separately. The results show that the performance is almost the same, with a fluctuation between 98% and 102%. Sometimes, symbols even perform slightly faster than strings.

In conclusion, I believe that your PR has a minimal impact on performance.

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	85.8 kB (+19 B)	32.7 kB (+69 B)	29.5 kB (+103 B)
vue.global.prod.js	132 kB (+19 B)	49.4 kB (+58 B)	44.3 kB (+20 B)

Usages

Name	Size	Gzip	Brotli
createApp	47.8 kB (+60 B)	18.9 kB (+11 B)	17.2 kB (+27 B)
createSSRApp	50.6 kB (+60 B)	20 kB (+21 B)	18.2 kB (+17 B)
defineCustomElement	50.2 kB (+60 B)	19.6 kB (+14 B)	17.9 kB (+11 B)
overall	61.2 kB (+39 B)	23.7 kB (+13 B)	21.6 kB (+7 B)