@langchain/vue

Vue SDK for building AI-powered applications with LangChain and LangGraph. Provides a useStream composable that manages streaming, state, branching, and interrupts using Vue's reactivity system.

Installation

npm install @langchain/vue @langchain/core

Peer dependencies: vue (^3.0.0), @langchain/core (^1.0.1)

Quick Start

<script setup lang="ts">
import { useStream } from "@langchain/vue";

const { messages, submit, isLoading } = useStream({
  assistantId: "agent",
  apiUrl: "http://localhost:2024",
});
</script>

<template>
  <div>
    <div v-for="(msg, i) in messages.value" :key="msg.id ?? i">
      {{ msg.content }}
    </div>

    <button
      :disabled="isLoading.value"
      @click="submit({ messages: [{ type: 'human', content: 'Hello!' }] })"
    >
      Send
    </button>
  </div>
</template>

useStream Options

Option	Type	Description
assistantId	string	Required. The assistant/graph ID to stream from.
apiUrl	string	Base URL of the LangGraph API.
client	Client	Pre-configured Client instance (alternative to apiUrl).
messagesKey	string	State key containing messages. Defaults to "messages".
initialValues	StateType	Initial state values before any stream data arrives.
fetchStateHistory	boolean \| { limit: number }	Fetch thread history on stream completion. Enables branching.
throttle	boolean \| number	Throttle state updates for performance.
onFinish	(state, error?) => void	Called when the stream completes.
onError	(error, state?) => void	Called on stream errors.
onThreadId	(threadId) => void	Called when a new thread is created.
onUpdateEvent	(event) => void	Receive update events from the stream.
onCustomEvent	(event) => void	Receive custom events from the stream.
onStop	() => void	Called when the stream is stopped by the user.

Return Values

All reactive properties are Vue computed or ref values.

Property	Type	Description
values	ComputedRef<StateType>	Current graph state.
messages	ComputedRef<Message[]>	Messages from the current state.
isLoading	Ref<boolean>	Whether a stream is currently active.
error	ComputedRef<unknown>	The most recent error, if any.
interrupt	ComputedRef<Interrupt \| undefined>	Current interrupt requiring user input.
branch	Ref<string>	Active branch identifier.
submit(values, options?)	function	Submit new input to the graph. When called while a stream is active, the run is created on the server with multitaskStrategy: "enqueue" and queued automatically.
stop()	function	Cancel the active stream.
setBranch(branch)	function	Switch to a different conversation branch.
getMessagesMetadata(msg, index?)	function	Get branching and checkpoint metadata for a message.
switchThread(id)	(id: string \| null) => void	Switch to a different thread. Pass null to start a new thread on next submit.
queue.entries	Ref<ReadonlyArray<QueueEntry>>	Pending server-side runs. Each entry has id (server run ID), values, options, and createdAt.
queue.size	Ref<number>	Number of pending runs on the server.
queue.cancel(id)	(id: string) => Promise<boolean>	Cancel a pending run on the server by its run ID.
queue.clear()	() => Promise<void>	Cancel all pending runs on the server.

Type Safety

Provide your state type as a generic parameter:

<script setup lang="ts">
import { useStream } from "@langchain/vue";
import type { BaseMessage } from "langchain";

interface MyState {
  messages: BaseMessage[];
  context?: string;
}

const { messages, submit } = useStream<MyState>({
  assistantId: "my-graph",
  apiUrl: "http://localhost:2024",
});
</script>

Typed Interrupts

<script setup lang="ts">
import { useStream } from "@langchain/vue";
import type { BaseMessage } from "langchain";

const { interrupt, submit } = useStream<
  { messages: BaseMessage[] },
  { InterruptType: { question: string } }
>({
  assistantId: "my-graph",
  apiUrl: "http://localhost:2024",
});
</script>

Handling Interrupts

<script setup lang="ts">
import { useStream } from "@langchain/vue";
import type { BaseMessage } from "langchain";

const { messages, interrupt, submit } = useStream<
  { messages: BaseMessage[] },
  { InterruptType: { question: string } }
>({
  assistantId: "agent",
  apiUrl: "http://localhost:2024",
});
</script>

<template>
  <div>
    <div v-for="(msg, i) in messages.value" :key="msg.id ?? i">
      {{ msg.content }}
    </div>

    <div v-if="interrupt.value">
      <p>{{ interrupt.value.value.question }}</p>
      <button @click="submit(null, { command: { resume: 'Approved' } })">
        Approve
      </button>
    </div>

    <button
      @click="submit({ messages: [{ type: 'human', content: 'Hello' }] })"
    >
      Send
    </button>
  </div>
</template>

Branching

Enable conversation branching with fetchStateHistory: true:

<script setup lang="ts">
import { useStream } from "@langchain/vue";

const { messages, submit, getMessagesMetadata, setBranch } = useStream({
  assistantId: "agent",
  apiUrl: "http://localhost:2024",
  fetchStateHistory: true,
});
</script>

<template>
  <div>
    <div v-for="(msg, i) in messages.value" :key="msg.id ?? i">
      <p>{{ msg.content }}</p>

      <template v-if="getMessagesMetadata(msg, i)?.branchOptions">
        <button
          @click="() => {
            const meta = getMessagesMetadata(msg, i);
            const prev = meta.branchOptions[meta.branchOptions.indexOf(meta.branch) - 1];
            if (prev) setBranch(prev);
          }"
        >
          Previous
        </button>
        <button
          @click="() => {
            const meta = getMessagesMetadata(msg, i);
            const next = meta.branchOptions[meta.branchOptions.indexOf(meta.branch) + 1];
            if (next) setBranch(next);
          }"
        >
          Next
        </button>
      </template>
    </div>

    <button
      @click="submit({ messages: [{ type: 'human', content: 'Hello' }] })"
    >
      Send
    </button>
  </div>
</template>

Server-Side Queuing

When submit() is called while a stream is already active, the SDK automatically creates the run on the server with multitaskStrategy: "enqueue". The pending runs are tracked in queue and processed in order as each finishes:

<script setup lang="ts">
import { useStream } from "@langchain/vue";

const { messages, submit, isLoading, queue, switchThread } = useStream({
  assistantId: "agent",
  apiUrl: "http://localhost:2024",
});
</script>

<template>
  <div>
    <div v-for="(msg, i) in messages.value" :key="msg.id ?? i">
      {{ msg.content }}
    </div>

    <div v-if="queue.size.value > 0">
      <p>{{ queue.size.value }} message(s) queued</p>
      <button @click="queue.clear()">Clear Queue</button>
    </div>

    <button
      :disabled="isLoading.value"
      @click="submit({ messages: [{ type: 'human', content: 'Hello!' }] })"
    >
      Send
    </button>
    <button @click="switchThread(null)">New Thread</button>
  </div>
</template>

Switching threads via switchThread() cancels all pending runs and clears the queue.

Custom Transport

Instead of connecting to a LangGraph API, you can provide your own streaming transport. Pass a transport object instead of assistantId to use a custom backend:

<script setup lang="ts">
import { useStream, FetchStreamTransport } from "@langchain/vue";
import type { BaseMessage } from "langchain";

const {
  messages,
  submit,
  isLoading,
  branch,
  setBranch,
  getMessagesMetadata,
} = useStream<{ messages: BaseMessage[] }>({
  transport: new FetchStreamTransport({
    url: "https://my-api.example.com/stream",
  }),
  threadId: null,
  onThreadId: (id) => console.log("Thread created:", id),
});
</script>

<template>
  <div>
    <div v-for="(msg, i) in messages.value" :key="msg.id ?? i">
      <p>{{ msg.content }}</p>
      <span v-if="getMessagesMetadata(msg, i)?.streamMetadata">
        Node: {{ getMessagesMetadata(msg, i)?.streamMetadata?.langgraph_node }}
      </span>
    </div>

    <p>Current branch: {{ branch.value }}</p>

    <button
      :disabled="isLoading.value"
      @click="submit({ messages: [{ type: 'human', content: 'Hello!' }] })"
    >
      Send
    </button>
  </div>
</template>

The custom transport interface returns the same properties as the standard useStream composable, including getMessagesMetadata, branch, setBranch, switchThread, and all message/interrupt/subagent helpers. When using a custom transport, getMessagesMetadata returns stream metadata sent alongside messages during streaming; branch and setBranch provide local branch state management.

Playground

For complete end-to-end examples with full agentic UIs, visit the LangGraph Playground.

License

MIT