`defineModel` doesn't run if the same value is selected

[TheFlyer1983]

Vue version

3.4.36

Link to minimal reproduction

https://shorturl.at/I2MOA

Steps to reproduce

Select an option on the button to select, and then click the same option to deselect.

Expected:
The option should de-select.

Actual:
Nothing

What is expected?

When selecting the same option twice, it should select the option then deselect the option.

What is actually happening?

When selecting the same option twice, the original click selects the option but the second click doesn't do anything.

System Info

System:
    OS: macOS 14.5
    CPU: (8) arm64 Apple M1 Pro
    Memory: 73.73 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.14.0 - ~/.nvm/versions/node/v20.14.0/bin/node
    npm: 10.7.0 - ~/.nvm/versions/node/v20.14.0/bin/npm
    bun: 1.1.4 - /opt/homebrew/bin/bun
  Browsers:
    Brave Browser: 126.1.67.134
    Chrome: 127.0.6533.99
    Safari: 17.5

Any additional comments?

This worked previously on an older version of Vue: 3.4.16. Yesterday (6th August 2024) I ram npm install and it updated a patch version of Vue (3.4.36).

After that my button component stopped working correctly. I feel like this is a breaking change.

[liuseen-l]

This seems to be as expected, because when the selected state is clicked again, the value of modelValue does not change, so the set method is not triggered.

[liuseen-l]

This way you can achieve your needs：

[TheFlyer1983]

But this feels like a breaking change, because this worked in Vue 3.4.16, and was broken in a patch update between 3.4.16 and 3.4.36.

It originally worked as I expected it to work, and now has broken many instances in my application because of this change.

[edison1105]

related PR

[TheFlyer1983]

But surely how it used work was consistent with how set function worked in a writeable computed property?

If you select the same value via a writeable computed property it runs the set function regardless. The defineModel should really work the same way.

[liuseen-l]

I opened a PR to solve this problem, which contains some of my own opinions. @edison1105 Do you have time to take a look? thank you🫰