can't define property Symbol("$state"): Object is not extensible

[laszlokorte]

Describe the bug

Frozen objects can not be written into a $state().

If for example some external library creates objects that are frozen, these objects can not be written into a svelte $state since [email protected] because the proxy tries to extend the value object or array with additional properties.

This prevents to use such external libraries in combination with svelte, especially if the objects in questions are not easily cloneable/unfreezable - for example nested objects and arrays containing DOM nodes.

My concrete use-case is the partial.lenses library. Its an optics library that can be used to read and updated nested objects. It freezes all new objects by default. These objects can then not be stored inside a $state. It did however work until [email protected]

Reproduction

https://svelte-5-preview.vercel.app/#H4sIAAAAAAAACo1Ty2rDMBD8FSEKcSA4d5MESiFQKBR6rXtQ7HWqIq-EtE7bGP97JfnRmEDIwQ-tZkaz43XLK6nA8ey95Shq4Bl_NIavOP2asHAnUAR-7XRji1DZuMJKQ7sccyo0OmJKHvYW4Azu9fAFBTm2ZWQbCIhwVQ0WJDUyp2t48eBh_WRBkMTj3mp9BuzJyUmoBpasjWySVXIlP23mZIEai6zfSKsIS1qJCDZjUalb9tiOgXJwxZxjB2h4hNsN72-R7s0_B37ybYUxUE7OBvWhnMZDRtV5JoJ0nUiU5EPDRqlJQgF5y7764EiQ7ypazO4LMQgux9ZnlqYAjl4_SiYXeU6w2-2CSvvPNPK61fjmJtnTTHek-IbuG4Mr7W4WoOrP8XIxwcUnKKUXnrRZ_w8obiSahlgY5m3OCX4o5-wgscyimW0ItffVsXXPcEbg7qLu9ULF_wK1LmUloeRZmO7uo_sDJ_qskT0DAAA=

Logs

Uncaught TypeError: can't define property Symbol("$state"): Array is not extensible

  in App.svelte
    proxy proxy.js:63
    set proxy.js:297
    App App.svelte:422

System Info

[email protected]
Firefox 126.0.1

Severity

blocking an upgrade