fix(core): Make dispatchCustomEvent not throw if used with no callbac…

…ks (#7513)

langchain-core/src/callbacks/dispatch/web.ts

@@ -39,17 +39,11 @@ export async function dispatchCustomEvent(
   payload: any,
   config?: RunnableConfig
 ) {
-  const callbackManager = await getCallbackManagerForConfig(config);
-  const parentRunId = callbackManager?.getParentRunId();
-  // We want to get the callback manager for the parent run.
-  // This is a work-around for now to be able to dispatch adhoc events from
-  // within a tool or a lambda and have the metadata events associated
-  // with the parent run rather than have a new run id generated for each.
-  if (callbackManager === undefined || parentRunId === undefined) {
+  if (config === undefined) {
     throw new Error(
       [
         "Unable to dispatch a custom event without a parent run id.",
-        "This function can only be called from within an existing run (e.g.,",
+        `"dispatchCustomEvent" can only be called from within an existing run (e.g.,`,
         "inside a tool or a RunnableLambda).",
         `\n\nIf you continue to see this error, please import from "@langchain/core/callbacks/dispatch/web"`,
         "and explicitly pass in a config parameter.",
@@ -60,7 +54,11 @@ export async function dispatchCustomEvent(
       ].join(" ")
     );
   }
+  const callbackManager = await getCallbackManagerForConfig(config);
+  const parentRunId = callbackManager?.getParentRunId();
   // We pass parent id as the current run id here intentionally since events dispatch
   // from within things like RunnableLambda
-  await callbackManager.handleCustomEvent?.(name, payload, parentRunId);
+  if (callbackManager !== undefined && parentRunId !== undefined) {
+    await callbackManager.handleCustomEvent?.(name, payload, parentRunId);
+  }
 }

langchain-core/src/runnables/tests/runnable_stream_events_v2.test.ts

@@ -1950,14 +1950,17 @@ test("Runnable streamEvents method with simple tools", async () => {
   ]);
 });
 
-test("Runnable streamEvents method with a custom event", async () => {
+test("Runnable methods with a custom event", async () => {
   const lambda = RunnableLambda.from(
     async (params: { x: number; y: string }, config) => {
       await dispatchCustomEvent("testEvent", { someval: "test" }, config);
       await dispatchCustomEvent("testEvent", { someval: "test2" }, config);
       return JSON.stringify({ x: params.x, y: params.y });
     }
   );
+  // Invoke shouldn't fail
+  const res = await lambda.invoke({ x: 1, y: "2" });
+  expect(res).toEqual(JSON.stringify({ x: 1, y: "2" }));
   const events = [];
   const eventStream = await lambda.streamEvents(
     { x: 1, y: "2" },