bridge-js

BridgeJS

BridgeJS is a code-generation layer in JavaScriptKit that makes Swift–JavaScript interop faster and easier than raw JSObject/JSValue: you declare the API shape in Swift (or TypeScript), and the tool generates glue code. Two directions: export Swift to JavaScript and import JavaScript into Swift.

Referencing official docs

When you need details, read DocC from the checked-out JavaScriptKit repository: Sources/JavaScriptKit/Documentation.docc/ when inside the JavaScriptKit repo, or .build/checkouts/JavaScriptKit/Sources/JavaScriptKit/Documentation.docc/ when in a project that depends on JavaScriptKit.

Two directions

• Export Swift: Use @JS (and @JS(namespace:enumStyle:identityMode:)) on functions, classes, structs, enums, closures, protocols, etc. JavaScript then calls into your Swift code. See references/exporting.md.
• Import JavaScript: (1) Declare bindings in Swift with @JSFunction, @JSClass, @JSGetter, @JSSetter; use @JSGetter(from: .global) for globals like document/console; inject other implementations via getImports(). See references/importing.md. (2) Or use bridge-js.d.ts to generate the same Swift bindings. See references/importing-ts.md.

Key concepts

• Type mapping: Primitives, Optional ↔ null, JSUndefinedOr ↔ undefined, arrays, Record<string, V> ↔ [String: V], JSTypedArray<T> ↔ TypedArray (by reference), unbridged → JSObject/JSValue. See references/types.md if present.
• Semantics: classes, protocols, JSTypedArray, and closures cross by reference; structs, enums, and plain arrays cross by copy.
• Errors: Only throws(JSException) is supported at the bridge; plain throws is not.
• Async: Exported async functions/methods/closures become Promise-returning JS functions (require JavaScriptEventLoop.installGlobalExecutor()). Imported standalone @JSFunction cannot be async, but imported async callbacks (closure parameters) are supported.
• Preview interfaces: For previewing d.ts → Swift locally, run the ts2swift script from the checked-out JavaScriptKit: from a project that depends on JavaScriptKit use node .build/checkouts/JavaScriptKit/Plugins/BridgeJS/Sources/TS2Swift/JavaScript/bin/ts2swift.js <input.d.ts> [options]; Run with --help for usage.
• Closures: Use JSTypedClosure when passing or returning Swift closures to JS, and call release() when the closure is no longer needed by JS. Plain Swift closure types also work as parameters/returns, released automatically via FinalizationRegistry. Closure signatures may be throws(JSException) and/or async. When receiving callbacks from JS (e.g. imported APIs), use regular closure types in Swift ((Args) -> Return).

References

• Project setup and config
• Exporting Swift to JS
• Importing JS into Swift (macros)
• Generating from TypeScript
• Supported types (optional)
• Testing
• Limitations