Function setContextVariable

Set a context variable. Context variables are scoped to any child runnables called by the current runnable, or globally if set outside of any runnable.

Remarks

This function is only supported in environments that support AsyncLocalStorage, including Node.js, Deno, and Cloudflare Workers.

Example

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({});
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