helpers.md

Message Helpers

Streaming Responses

anthropic.messages.stream({ … }, options?): MessageStream

anthropic.messages.stream() returns a MessageStream, which emits events, has an async iterator, and exposes helper methods to accumulate stream events into a convenient shape and make it easy to reason about the conversation.

Alternatively, you can use anthropic.messages.create({ stream: true, … }) which returns an async iterable of the chunks in the stream and uses less memory (most notably, it does not accumulate a message object for you).

If you need to cancel a stream, you can break from a for await loop or call stream.abort().

See an example of streaming helpers in action in examples/streaming.ts.

MessageStream API

Events

.on('connect', () => …)

The first event that is fired when the connection with the Anthropic API is established.

.on('streamEvent', (event: MessageStreamEvent, snapshot: Message) => …)

The event fired when a stream event is received from the API. Not fired when it is not streaming. The snapshot returns an accumulated Message which is progressively built-up over events.

.on('text', (textDelta: string, textSnapshot: string) => …)

The event fired when a text delta is sent by the API. The second parameter returns a textSnapshot.

.on('inputJson', (patialJson: string, jsonSnapshot: unknown) => …)

The event fired when a json delta is sent by the API. The second parameter returns a jsonSnapshot.

.on('message', (message: Message) => …)

The event fired when a message is done being streamed by the API. Corresponds to the message_stop SSE event.

.on('contentBlock', (content: ContentBlock) => …)

The event fired when a content block is done being streamed by the API. Corresponds to the content_block_stop SSE event.

.on('finalMessage', (message: Message) => …)

The event fired for the final message. Currently this is equivalent to the message event, but is fired after it.

.on('error', (error: AnthropicError) => …)

The event fired when an error is encountered while streaming.

.on('abort', (error: APIUserAbortError) => …)

The event fired when the stream receives a signal to abort.

.on('end', () => …)

The last event fired in the stream.

Methods

.abort()

Aborts the runner and the streaming request, equivalent to .controller.abort(). Calling .abort() on a MessageStream will also abort any in-flight network requests.

await .done()

An empty promise which resolves when the stream is done.

.currentMessage

Returns the current state of the message that is being accumulated, or undefined if there is no such message.

await .finalMessage()

A promise which resolves with the last message received from the API. Throws if no such message exists.

await .finalText()

A promise which resolves with the text of the last message received from the API.

Fields

.messages

A mutable array of all messages in the conversation.

.controller

The underlying AbortController for the runner.