setContextVariable

import { RunnableLambda } from "@langchain/core/runnables";
import {
  getContextVariable,
  setContextVariable
} from "@langchain/core/context";

const nested = RunnableLambda.from(() => {
  // "bar" because it was set by a parent
  console.log(getContextVariable("foo"));

  // Override to "baz", but only for child runnables
  setContextVariable("foo", "baz");

  // Now "baz", but only for child runnables
  return getContextVariable("foo");
});

const runnable = RunnableLambda.from(async () => {
  // Set a context variable named "foo"
  setContextVariable("foo", "bar");

  const res = await nested.invoke({});

  // Still "bar" since child changes do not affect parents
  console.log(getContextVariable("foo"));

  return res;
});

// undefined, because context variable has not been set yet
console.log(getContextVariable("foo"));

// Final return value is "baz"
const result = await runnable.invoke({});