FunctionBackendAdapter

Defined in: backend-browser/src/function.ts:168

Generic function-based backend adapter.

Accepts async functions for execute and stream operations, making it easy to:

• Create custom backends from simple functions
• Write integration tests with controlled behavior
• Wrap external services or APIs
• Create mock backends with specific responses

Example

// Simple echo backend
const echoBackend = new FunctionBackendAdapter({
  execute: async (request) => ({
    message: { role: 'assistant', content: `Echo: ${request.messages[0]?.content}` },
    finishReason: 'stop',
    metadata: { requestId: request.metadata.requestId, provenance: {} },
  }),
});

// Backend with streaming
const streamingBackend = new FunctionBackendAdapter({
  execute: async (request) => ({ ... }),
  executeStream: async function* (request) {
    yield { type: 'start', sequence: 0 };
    yield { type: 'content', sequence: 1, delta: 'Hello', role: 'assistant' };
    yield { type: 'done', sequence: 2, finishReason: 'stop', message: { ... } };
  },
});

Type Parameters

TRequest

TRequest = IRChatRequest

TResponse

TResponse = IRChatResponse

Implements

• BackendAdapter<TRequest, TResponse>

Constructors

Constructor

new FunctionBackendAdapter<TRequest, TResponse>(config): FunctionBackendAdapter<TRequest, TResponse>

Defined in: backend-browser/src/function.ts:187

Create a new function-based backend adapter.

Parameters

config

FunctionBackendConfig<TRequest, TResponse>

Configuration with execute function and optional customizations

Returns

FunctionBackendAdapter<TRequest, TResponse>

Properties

metadata

readonly metadata: AdapterMetadata

Defined in: backend-browser/src/function.ts:172

Adapter metadata for identification and capabilities.

Implementation of

BackendAdapter.metadata

Methods

estimateCost()

estimateCost(request): Promise<number | null>

Defined in: backend-browser/src/function.ts:322

Estimate cost for a request.

Parameters

request

IRChatRequest

Returns

Promise<number | null>

Implementation of

BackendAdapter.estimateCost

---

execute()

execute(request, signal?): Promise<IRChatResponse>

Defined in: backend-browser/src/function.ts:270

Execute non-streaming chat completion request.

Parameters

request

IRChatRequest

signal?

AbortSignal

Returns

Promise<IRChatResponse>

Implementation of

BackendAdapter.execute

---

executeStream()

executeStream(request, signal?): IRChatStream

Defined in: backend-browser/src/function.ts:295

Execute streaming chat completion request.

Parameters

request

IRChatRequest

signal?

AbortSignal

Returns

IRChatStream

Implementation of

BackendAdapter.executeStream

---

fromIR()

fromIR(request): TRequest

Defined in: backend-browser/src/function.ts:243

Convert IR request to provider-specific format. Default implementation returns the request unchanged.

Parameters

request

IRChatRequest

Returns

TRequest

Implementation of

BackendAdapter.fromIR

---

healthCheck()

healthCheck(): Promise<boolean>

Defined in: backend-browser/src/function.ts:315

Health check to verify backend is available.

Returns

Promise<boolean>

Implementation of

BackendAdapter.healthCheck

---

listModels()

listModels(options?): Promise<ListModelsResult>

Defined in: backend-browser/src/function.ts:329

List available models.

Parameters

options?

ListModelsOptions

Returns

Promise<ListModelsResult>

Implementation of

BackendAdapter.listModels

---

toIR()

toIR(response, originalRequest, latencyMs): IRChatResponse

Defined in: backend-browser/src/function.ts:251

Convert provider response to IR format. Default implementation returns the response with updated metadata.

Parameters

response

TResponse

originalRequest

IRChatRequest

latencyMs

number

Returns

IRChatResponse

Implementation of

BackendAdapter.toIR