René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Looking for API ideas: Typed closure handle for BridgeJS","articleBody":"## Summary\n\nBridgeJS needs a typed closure handle type that preserves object identity across the Swift/JS bridge. We're looking for community input on naming.\n\n## Background\n\nJavaScriptKit already has `JSClosure` for untyped closures:\n\n```swift\nlet closure = JSClosure { args -\u003e JSValue in\n    // ...\n}\n```\n\nFor BridgeJS, we need a **typed** variant with a generic parameter for the function signature. This enables type-safe declarations like:\n\n```swift\n@JSFunction func addEventListener(_ type: String, _ listener: (MessageEvent) -\u003e Void)\n```\n\nThe typed closure handle is essential for APIs like `addEventListener`/`removeEventListener` that require stable object identity, passing the same closure reference to both calls.\n\n## Related issues\n\n- https://github.com/swiftwasm/JavaScriptKit/issues/536\n  - We need the explicit handle to allow manually releasing JS-passed closures \n- https://github.com/swiftwasm/JavaScriptKit/issues/540\n\n## Constraints\n\n1. Must coexist with `JSClosure`: we can't simply make `JSClosure\u003cT\u003e` generic (breaking change)\n2. Explicit conversion required: Swift doesn't support implicit conversion from closure literals, so users will write the type name frequently\n\n## Candidates\n\n### 1. Nested type: `JSClosure.Typed\u003cT\u003e`\n\n```swift\n@JSClass struct JSHTMLElement {\n    @JSFunction func addEventListener(_ type: String, _ listener: JSClosure.Typed\u003c(MessageEvent) -\u003e Void\u003e)\n    @JSFunction func removeEventListener(_ type: String, _ listener: JSClosure.Typed\u003c(MessageEvent) -\u003e Void\u003e)\n}\n\nlet handler = JSClosure.Typed\u003c(MessageEvent) -\u003e Void\u003e { event in\n    print(event.data)\n}\ndocument.addEventListener(\"load\", handler)\ndocument.removeEventListener(\"load\", handler)\n\n@JSFunction func requestAnimationFrame(_ callback: JSOneshotClosure.Typed\u003c(Double) -\u003e Void\u003e)\n\nrequestAnimationFrame(JSOneshotClosure.Typed { timestamp in\n  print(timestamp)\n})\n```\n\n- Clear relationship to `JSClosure`\n- Discoverable via autocomplete\n- Verbose (15 characters)\n\n\n### 2. `JSTypedClosure\u003cT\u003e`\n\n\n```swift\n@JSClass struct JSHTMLElement {\n    @JSFunction func addEventListener(_ type: String, _ listener: JSTypedClosure\u003c(MessageEvent) -\u003e Void\u003e)\n    @JSFunction func removeEventListener(_ type: String, _ listener: JSTypedClosure\u003c(MessageEvent) -\u003e Void\u003e)\n}\n\nlet handler = JSTypedClosure\u003c(MessageEvent) -\u003e Void\u003e { event in\n    print(event.data)\n}\ndocument.addEventListener(\"load\", handler)\ndocument.removeEventListener(\"load\", handler)\n\n@JSFunction func requestAnimationFrame(_ callback: JSTypedClosure\u003c(Double) -\u003e Void\u003e)\n\nrequestAnimationFrame(JSTypedClosure.oneshot { timestamp in\n  print(timestamp)\n})\n```\n\n### 3. `JSCallback\u003cT\u003e`\n\n\n```swift\n@JSClass struct JSHTMLElement {\n    @JSFunction func addEventListener(_ type: String, _ listener: JSCallback\u003c(MessageEvent) -\u003e Void\u003e)\n    @JSFunction func removeEventListener(_ type: String, _ listener: JSCallback\u003c(MessageEvent) -\u003e Void\u003e)\n}\n\nlet handler = JSCallback\u003c(MessageEvent) -\u003e Void\u003e { event in\n    print(event.data)\n}\ndocument.addEventListener(\"load\", handler)\ndocument.removeEventListener(\"load\", handler)\n\n@JSFunction func requestAnimationFrame(_ callback: JSCallback.Oneshot\u003c(Double) -\u003e Void\u003e)\n\nrequestAnimationFrame(JSCallback.Oneshot { timestamp in\n  print(timestamp)\n})\n```\n\n### 3. [Need your input]\n","author":{"url":"https://github.com/kateinoigakukun","@type":"Person","name":"kateinoigakukun"},"datePublished":"2026-01-28T11:45:43.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/541/JavaScriptKit/issues/541"}