LlamaIndex Workflows TS

🌊 is a simple, lightweight workflow engine, in TypeScript.


- Minimal core API (<=2kb)
- 100% Type safe
- Event-driven, stream oriented programming
- Support multiple JS runtime/framework

Usage

``shell
npm i @llamaindex/workflow-core

yarn add @llamaindex/workflow-core

pnpm add @llamaindex/workflow-core

bun add @llamaindex/workflow-core

deno add npm:@llamaindex/workflow-core
`

$3

`ts
import { workflowEvent } from "@llamaindex/workflow-core";

const startEvent = workflowEvent();
const stopEvent = workflowEvent<1 | -1>();
`

$3

`ts
import { createWorkflow } from "@llamaindex/workflow-core";

const convertEvent = workflowEvent();

const workflow = createWorkflow();

workflow.handle([startEvent], (start) => {
return convertEvent.with(Number.parseInt(start.data, 10));
});
workflow.handle([convertEvent], (convert) => {
return stopEvent.with(convert.data > 0 ? 1 : -1);
});
`

$3

`ts
import { pipeline } from "node:stream/promises";

const { stream, sendEvent } = workflow.createContext();
sendEvent(startEvent.with());
const result = await pipeline(stream, async function (source) {
for await (const event of source) {
if (stopEvent.include(event)) {
return "stop received!";
}
}
});
console.log(result); // stop received!
// or
const allEvents = await stream.until(stopEvent).toArray();
`

$3

There are helper functions to make working with workflows even simpler:

`ts
import {
runWorkflow,
runAndCollect,
runWorkflowWithFilter,
} from "@llamaindex/workflow-core/stream/run";

// Run workflow and get final result
const result = await runWorkflow(workflow, startEvent.with("42"), stopEvent);

// Run workflow and collect all events
const allEvents = await runAndCollect(
workflow,
startEvent.with("42"),
stopEvent,
);
`

$3

By default, we provide a simple fan-out utility to run multiple workflows in parallel

- context.sendEvent will emit a new event to current workflow
- context.stream will return a stream of events emitted by the sub-workflow

`ts
let condition = false;
workflow.handle([startEvent], async (context, start) => {
const { sendEvent, stream } = context;
for (let i = 0; i < 10; i++) {
sendEvent(convertEvent.with(i));
}
// You define the condition to stop the workflow
const results = await stream
.until(() => condition)
.filter(convertStopEvent)
.toArray();
console.log(results.length); // 10
return stopEvent.with();
});

workflow.handle([convertEvent], (convert) => {
if (convert.data === 9) {
condition = true;
}
return convertStopEvent.with(/ ... /);
});
`

$3

Workflow is event-driven, you can use any stream API to handle the workflow like rxjs

`ts
import { from, pipe } from "rxjs";

const { stream, sendEvent } = workflow.createContext();

from(stream)
.pipe(filter((ev) => eventSource(ev) === messageEvent))
.subscribe((ev) => {
console.log(ev.data);
});

sendEvent(fileParseWorkflow.startEvent(directory));
`

$3

Workflow can be used as middleware in any server framework, like express, hono, fastify, etc.

`ts
import { Hono } from "hono";
import { serve } from "@hono/node-server";
import { createHonoHandler } from "@llamaindex/workflow-core/interrupter/hono";
import {
agentWorkflow,
startEvent,
stopEvent,
} from "../workflows/tool-call-agent.js";

const app = new Hono();

app.post(
"/workflow",
createHonoHandler(
agentWorkflow,
async (ctx) => startEvent(await ctx.req.text()),
stopEvent,
),
);

serve(app, ({ port }) => {
console.log(Server started at http://localhost:${port});
});
`

$3

You can use signal in the context parameter to handle error

`ts
workflow.handle([convertEvent], (context) => {
const { signal } = context;

signal.onabort = () => {
console.error("error in convert event:", abort.reason);
};
});
`

$3

Workflow handlers receive the context as the first parameter, providing access to sendEvent, stream, and signal.

`ts
workflow.handle([startEvent], async (context) => {
const { sendEvent, stream, signal } = context;
// Use context properties directly
sendEvent(processEvent.with());
});
`

Middleware

$3

Adding a state property to the workflow context, which returns a state object, each state is linked to the workflow
context.

`ts
import { createStatefulMiddleware } from "@llamaindex/workflow-core/middleware/state";

const { withState } = createStatefulMiddleware(() => ({
pendingTasks: new Set>(),
}));

const workflow = withState(createWorkflow());

workflow.handle([startEvent], (context) => {
const { state } = context;
state.pendingTasks.add(
new Promise((resolve) => {
setTimeout(() => {
resolve();
}, 100);
}),
);
});

const { state } = workflow.createContext();
`

You can also create a state with input:

`ts
const { withState } = createStatefulMiddleware((input: { id: string }) => ({
id: input.id,
}));

const workflow = withState(createWorkflow());
const { state } = workflow.createContext({ id: "1" });
`

withState also supports snapshot, you can use snapshot to save the state of the workflow, and resume to restore the state of the workflow.

`ts
const { snapshot, resume } = workflow.createContext();

// create snapshot
const snapshotData = await snapshot();

// resume workflow from snapshot
const { stream, sendEvent } = workflow.resume(snapshotData);
sendEvent(humanResponseEvent.with("hello"));
`

$3

Make first parameter of handler to be sendEvent and its type safe and runtime safe
when you create a workflow using withValidation.

`ts
// before:
workflow.handle([startEvent], (start) => {});
// after:
workflow.handle([startEvent], (sendEvent, start) => {});
`

`ts
import { withValidation } from "@llamaindex/workflow-core/middleware/validation";

const startEvent = workflowEvent();
const disallowedEvent = workflowEvent({
debugLabel: "disallowed",
});
const parseEvent = workflowEvent();
const stopEvent = workflowEvent();
const workflow = withValidation(createWorkflow(), [
[[startEvent], [stopEvent]],
[[startEvent], [parseEvent]],
]);

workflow.strictHandle([startEvent], (sendEvent, start) => {
sendEvent(
disallowedEvent.with(), // <-- ❌ Type Check Failed, Runtime Error
);
sendEvent(parseEvent.with("")); // <-- ✅
sendEvent(stopEvent.with(1)); // <-- ✅
});
`

$3

Adds tracing capabilities to your workflow, allowing you to monitor/decorate handler and debug event flows easily.

When enabled,
it collects events based on the directed graph of the runtime and provide lifecycle hooks for each handler.

`ts
import {
withTraceEvents,
runOnce,
} from "@llamaindex/workflow-core/middleware/trace-events";

const workflow = withTraceEvents(createWorkflow());

workflow.handle(
[messageEvent],
runOnce(() => {
console.log("This message handler will only run once");
}),
);

workflow.handle([startEvent], (context) => {
context.sendEvent(messageEvent.with());
context.sendEvent(messageEvent.with());
});

{
const { sendEvent } = workflow.createContext();
sendEvent(startEvent.with());
sendEvent(messageEvent.with());
// This message handler will only run once!
}
{
const { sendEvent } = workflow.createContext();
// For each new context, the decorator is isolated.
sendEvent(startEvent.with());
sendEvent(messageEvent.with());
// This message handler will only run once!
}
`

#### workflow.substream(target, stream)

You can use substream to create a substream from the workflow context,
which will only emit events that are emitted by the target event.

`ts
const ev = startEvent.with();
const { sendEvent, stream } = workflow.createContext();
sendEvent(ev);
sendEvent(messageEvent.with()); // <- this will not be included in the substream
const substream = workflow.substream(ev, stream);
`

This is helpful when you have async requests, and you want to track the events that are emitted by the target event.

For example:

- Parallel requests

`ts
workflow.handle([startEvent], async (context) => {
const { sendEvent, stream } = context;
const ev = networkRequestEvent.with();
sendEvent(networkRequestEvent);
const responses = await collect(workflow.substream(ev, stream));
});

sendEvent(startEvent.with());
sendEvent(startEvent.with());
`

#### createHandlerDecorator

You can create your own handler decorator to modify the behavior of the handler.

`ts
import { createHandlerDecorator } from "@llamaindex/workflow-core/middleware/trace-events";

const noop: (...args: any[]) => void = function noop() {};
export const runOnce = createHandlerDecorator({
debugLabel: "onceHook",
getInitialValue: () => false,
onBeforeHandler: (handler, handlerContext, tracked) =>
tracked ? noop : handler,
onAfterHandler: () => true,
});
`

#### HandlerContext

The HandlerContext includes the runtime information of the handler in the directed graph of the workflow.

`ts
type BaseHandlerContext = {
// ... some other properties are hidden
handler: Handler[], any>;
inputEvents: WorkflowEvent[];
// events data that are accepted by the handler
inputs: WorkflowEventData[];
// events data that are emitted by the handler
outputs: WorkflowEventData[];

//#region linked list data structure
prev: HandlerContext;
next: Set;
root: HandlerContext;
//#endregion
};

type SyncHandlerContext = BaseHandlerContext & {
async: false;
pending: null;
};

type AsyncHandlerContext = BaseHandlerContext & {
async: true;
pending: Promise | void> | null;
};

type HandlerContext = AsyncHandlerContext | SyncHandlerContext;
`

For example, when you send two startEvent events, and send messageEvent twice (once in the handler and once in the global),
the HandlerContext from root to leaf is:

`ts
let once = false;
workflow.handle([startEvent], (context) => {
const { sendEvent } = context;
if (once) {
return;
}
once = true;
sendEvent(messageEvent.with());
});
const { sendEvent } = workflow.createContext();
sendEvent(startEvent.with());
sendEvent(startEvent.with());
sendEvent(messageEvent.with());
`

`
rootHandlerContext(0)
├── startEventContext(0)
│ └── messageEventContext(0)
├── startEventContext(1)
└── messageEventContext(1)
``

You can use any directed graph library to visualize the directed graph of the workflow.

Related Packages

- Python Workflows