#Runtime Domain

The Runtime domain handles JavaScript execution and evaluation.

#Methods

#Runtime.evaluate

Evaluates a JavaScript expression.

Parameters:

• expression (string): JavaScript expression to evaluate
• returnByValue (boolean, optional): Whether to return the value

Returns:

• result: Evaluation result (must be the value of the expression; e.g. 1+2 → 3, globalThis.x != undefined → true/false). Required for React DevTools frontend initialization when used from React Native.

#Runtime.addBinding

Registers a binding name. When the client (e.g. app) later invokes that binding, the backend sends a Runtime.bindingCalled event. Used by React DevTools (Fusebox) for messaging between the DevTools frontend and the React Native app.

Parameters:

• name (string): Binding name (e.g. "react-devtools")

Returns:

• (empty on success)

#Runtime.getProperties

Returns properties of an object (by objectId). Used when the user expands an object in the Console. Implemented in react-native-inspector.

Parameters:

• objectId (string): Object ID (from a RemoteObject)

Returns:

• result: Array of PropertyDescriptor (each has name, value as RemoteObject, etc.)

#Runtime.releaseObject

Releases an object so the backend can drop its reference. DevTools calls this when an object is no longer needed. Implemented in react-native-inspector.

Parameters:

• objectId (string): Object ID to release

Returns:

• (empty on success)

#Runtime.enable

Enables the Runtime domain. When the frontend sends this (e.g. when DevTools connects), the backend should send Runtime.executionContextCreated so the frontend can associate console messages with a context. Implemented in react-native-inspector (no response body; backend sends the event).

#Runtime.callFunctionOn

Calls a function. Not implemented in react-native-inspector.

Parameters:

• functionDeclaration (string): Function declaration to call
• objectId (string, optional): Object ID to call the function on

Returns:

• result: Call result

#Events

#Runtime.consoleAPICalled

Emitted when a console API is called.

Parameters:

• type: Console message type (log, error, warn, info, debug)
• args: Console arguments
• timestamp: Timestamp

#Runtime.executionContextCreated

Emitted when a JavaScript execution context is created. The backend sends this when it receives Runtime.enable so the frontend can register the context before console messages arrive. Implemented in react-native-inspector.

Parameters:

• context: { id: number, origin: string, name?: string, auxData?: object } — at least id and origin (e.g. "react-native://").

#Runtime.bindingCalled

Emitted when the client invokes a binding previously registered with Runtime.addBinding. Used by React DevTools: the app calls the binding with a serialized message; the frontend receives this event and forwards it to the React DevTools UI.

Parameters:

• name (string): Binding name
• payload (string): Serialized message (e.g. JSON)
• executionContextId (number): Execution context ID

#Protocol details (wire format)

CDP messages are JSON. Commands: { "id": number, "method": "Domain.method", "params": object }. Responses: { "id": number, "result": object } or { "id": number, "error": { "code": number, "message": string } }. Events: { "method": "Domain.event", "params": object }. Full spec: Chrome DevTools Protocol — Runtime.

#Runtime.evaluate

• Request: { "id": number, "method": "Runtime.evaluate", "params": { "expression": string, "returnByValue": boolean? } }
• Response: { "id": number, "result": { "result": RemoteObject, "exceptionDetails"?: ExceptionDetails } } or { "id": number, "error": { "code", "message" } }
• RemoteObject: { "type": "string"|"number"|"boolean"|"object"|"undefined"|..., "value"?: any, "subtype"?: string, "description"?: string }. For React Native, the backend must return the evaluated value (e.g. true/false for expressions like globalThis.x != undefined).

#Runtime.addBinding

• Request: { "id": number, "method": "Runtime.addBinding", "params": { "name": string } }
• Response: { "id": number, "result": {} }

#Runtime.getProperties

• Request: { "id": number, "method": "Runtime.getProperties", "params": { "objectId": string } }
• Response: { "id": number, "result": { "result": PropertyDescriptor[] } }. Each descriptor has name, value (RemoteObject), and optionally configurable, enumerable, writable, get, set.

#Runtime.releaseObject

• Request: { "id": number, "method": "Runtime.releaseObject", "params": { "objectId": string } }
• Response: { "id": number, "result": {} }

#Runtime.enable

• Request: { "id"?: number, "method": "Runtime.enable", "params"?: {} } (often no id). Backend does not send a CDP response; it sends Runtime.executionContextCreated as an event so the frontend can register the context.

#Runtime.executionContextCreated (event)

• Event: { "method": "Runtime.executionContextCreated", "params": { "context": { "id": number, "origin": string, "name"?: string, "auxData"?: object } } }. Example: "context": { "id": 1, "origin": "react-native://" }.

#Runtime.bindingCalled (event)

• Event: { "method": "Runtime.bindingCalled", "params": { "name": string, "payload": string, "executionContextId": number } }
• Payload (React DevTools): The payload is a string. The app (or backend) must pass a JSON string of shape { "domain": string, "message": any }. The DevTools frontend parses it and dispatches message to listeners for that domain (e.g. "react-devtools"). The inner message format is defined by the React DevTools Fusebox bridge; we only relay the string.

Example (app → frontend): App calls the binding with JSON.stringify({ domain: 'react-devtools', message: { event: '...', payload: ... } }). The inspector sends a CDP event Runtime.bindingCalled with params.payload equal to that string. The frontend parses it and forwards message to the React DevTools UI.

#React Native (react-native-inspector)

The react-native-inspector package implements the following Runtime commands and events so that the Inspector (Console, React DevTools Components/Profiler) can work with the app:

Commands (frontend → backend):

• Runtime.enable — Backend sends Runtime.executionContextCreated (no response body).
• Runtime.evaluate — Must return the expression value (not undefined). Required for React DevTools (e.g. polling globalThis.__FUSEBOX_REACT_DEVTOOLS_DISPATCHER__ != undefined).
• Runtime.addBinding — Registers the binding name; the app receives a global function. When the app calls it, the inspector sends Runtime.bindingCalled.
• Runtime.getProperties — Returns properties for an object (Console expand).
• Runtime.releaseObject — Releases an object by objectId.

Events (backend → frontend):

• Runtime.executionContextCreated — Sent when Runtime.enable is received.
• Runtime.consoleAPICalled — Console log/warn/error etc.
• Runtime.bindingCalled — App invoked a binding (React DevTools messaging).

Not implemented: Runtime.callFunctionOn.

See React DevTools Components & Profiler for setup and "Implementation status and fixes."