defineModel is triggering update event, even if its value didn't actually change

[alann-sapone]

Vue version

3.4.27

Link to minimal reproduction

Minimal reproduction link

Steps to reproduce

Here, when I click on the button Apply value to model, I can see that the counter increases, even if the value is exactly the same.

What is expected?

I expected the same behavior as the one we had when the feature was still experimental : Only triggering an update when the value is actually different, not only when its assigned with any value

What is actually happening?

Setting a value always triggers the update:modelValue event, even if it didn't actually changed, which leads to useless reactivy, and even worse, duplicated API calls, etc...

System Info

System:
    OS: Linux 5.15 Ubuntu 22.04.4 LTS 22.04.4 LTS (Jammy Jellyfish)
    CPU: (24) x64 AMD Ryzen 9 3900X 12-Core Processor
    Memory: 11.37 GB / 15.57 GB
    Container: Yes
    Shell: 5.1.16 - /bin/bash
  Binaries:
    Node: 20.14.0 - /usr/bin/node
    npm: 10.7.0 - /usr/bin/npm
    pnpm: 9.0.6 - /usr/bin/pnpm
  npmPackages:
    vue: ^3.4.27 => 3.4.27

Any additional comments?

We actually updated our Vue version and removed all occurences of { local: true } because we had to fix some Vue bugs which were corrected in more mature versions.

Quick note: I'm aware that I could replace all occurrences of @update:something with a watch like
in this exemple. But the pain point is when your app is already having a lot of @update:something :).

[jh-leong]

Workaround: use https://vueuse.org/core/useVModel/#usevmodel (see the shouldEmit option)

[alann-sapone]

Actually, we migrated from useVModel to defineModel. But this is the same issue as the one I mentionned before : In our app, it means a huge refacto of our code. As I am not sure that this is the desired behaviour of defineModel, I think it's safer to open a ticket to challenge this implementation which changed from when it still was an experimental feature.

[alann-sapone]

@yangxiuxiu1115 : Hey there !
Thank you for your pull request opening :). Just wondering : Did you fix it because it wasn't the desired behavior ?

[yangxiuxiu1115]

Yes, a lot of these optimizations exist within vue, and I think maybe DefineModel shouldn't be special