Function entrypoint

Define a LangGraph workflow using the entrypoint function.

!!! warning "Beta" The Functional API is currently in beta and is subject to change.

Function signature

The wrapped function must accept at most two parameters. The first parameter is the input to the function. The second (optional) parameter is a LangGraphRunnableConfig object. If you wish to pass multiple parameters to the function, you can pass them as an object.

Helper functions

Streaming

To write data to the "custom" stream, use the getWriter function, or the LangGraphRunnableConfig.writer property.

State management

The getPreviousState function can be used to access the previous state that was returned from the last invocation of the entrypoint on the same thread id.

If you wish to save state other than the return value, you can use the entrypoint.final function.

Example: Using entrypoint and tasks

import { task, entrypoint } from "@langchain/langgraph";
import { MemorySaver } from "@langchain/langgraph-checkpoint";
import { interrupt, Command } from "@langchain/langgraph";

const composeEssay = task("compose", async (topic: string) => {
  await new Promise(r => setTimeout(r, 1000)); // Simulate slow operation
  return `An essay about ${topic}`;
});

const reviewWorkflow = entrypoint({
  name: "review",
  checkpointer: new MemorySaver()
}, async (topic: string) => {
  const essay = await composeEssay(topic);
  const humanReview = await interrupt({
    question: "Please provide a review",
    essay
  });
  return {
    essay,
    review: humanReview
  };
});

// Example configuration for the workflow
const config = {
  configurable: {
    thread_id: "some_thread"
  }
};

// Topic for the essay
const topic = "cats";

// Stream the workflow to generate the essay and await human review
for await (const result of reviewWorkflow.stream(topic, config)) {
  console.log(result);
}

// Example human review provided after the interrupt
const humanReview = "This essay is great.";

// Resume the workflow with the provided human review
for await (const result of reviewWorkflow.stream(new Command({ resume: humanReview }), config)) {
  console.log(result);
}
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Example: Accessing the previous return value

import { entrypoint, getPreviousState } from "@langchain/langgraph";
import { MemorySaver } from "@langchain/langgraph-checkpoint";

const accumulator = entrypoint({
  name: "accumulator",
  checkpointer: new MemorySaver()
}, async (input: string) => {
  const previous = getPreviousState<number>();
  return previous !== undefined ? `${previous } ${input}` : input;
});

const config = {
  configurable: {
    thread_id: "some_thread"
  }
};
await accumulator.invoke("hello", config); // returns "hello"
await accumulator.invoke("world", config); // returns "hello world"
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Example: Using entrypoint.final to save a value

import { entrypoint, getPreviousState } from "@langchain/langgraph";
import { MemorySaver } from "@langchain/langgraph-checkpoint";

const myWorkflow = entrypoint({
  name: "accumulator",
  checkpointer: new MemorySaver()
}, async (num: number) => {
  const previous = getPreviousState<number>();

  // This will return the previous value to the caller, saving
  // 2 * num to the checkpoint, which will be used in the next invocation
  // for the `previous` parameter.
  return entrypoint.final({
    value: previous ?? 0,
    save: 2 * num
  });
});

const config = {
  configurable: {
    thread_id: "some_thread"
  }
};

await myWorkflow.invoke(3, config); // 0 (previous was undefined)
await myWorkflow.invoke(1, config); // 6 (previous was 3 * 2 from the previous invocation)
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