microsoft
fix: Observable properties passed from an element to another without an initializer are not responsive in Safari 26
🐛 Bug Report In Safari 26, observable properties passed from one FASTElement to another do not update reactively under certain conditions.
💻 Repro or Code Sample https://stackblitz.com/edit/typescript-7vs2owmc?file=index.ts
🤔 Expected Behavior Both prop1 and prop2 should update reactively in my-element-two when their corresponding values in my-element change.
😯 Current Behavior In Safari 26, prop1 updates as expected, but prop2 (anotherProp) does not reflect changes reactively in my-element-two.
💁 Possible Solution This may be related to Safari’s handling of property bindings or shadow DOM updates. We have seen that properties marked from boundObservables https://github.com/microsoft/fast/blob/15f32c3883b3ddbe1d5f428e5fbeb997b3becc55/packages/web-components/fast-element/src/components/element-controller.ts#L259 do work, and all others don't
🔦 Context This issue affects component composition and data flow in FASTElement-based applications when targeting Safari users. It limits the reliability of reactive bindings between components and for our app; it requires us to manually initialize every property passed by a parent
🌍 Your Environment
OS & Device: macOS 26.0 on MacMini Browser: Apple Safari Version: Safari 26
Same problem for me
OS & Device: macOS 26.0 on Macbook Pro Browser: Apple Safari Version: Safari 26
Same problem for me
OS & Device: macOS 26.0 on Macbook Pro Browser: Apple Safari Version: Safari 26
