Superjson Inngest Middleware

function.ts

/*
Superjson is awesome, but here are a few considerations for using transformers in middleware are:
1 - Building multi-language flows (TS + Python) become tricky if you're serializing events. 
2 - You're locked into superjson for long running jobs, so if you want to change a serialization format, you'll have to support backcompat.
3 - Pass through TypeScript types for transformers like this aren't yet well supported. You may need to cast http://step.run return values until we fix that up (we plan to).
*/
import { Inngest } from 'inngest';
import { superjsonMiddleware } from './superjson-middleware';

const inngest = new Inngest({
  id: 'demo-app',
  middleware: [superjsonMiddleware]
});

export default inngest.createFunction(
  { id: 'hello-world' },
  { event: 'demo/event.sent' },
  async ({ event, step }) => {

    // As of Inngest TS SDK v3.19.22 types modified via middleware 
    // do not pass through from the deserialization.
    // To get around this, each return type must be cast "as" for types to work 
    // NOTE - This will be fixed in a future version
    const result = await step.run('first', () => {
      return { now: new Date() };
    }) as unknown as { now: Date} ;

    console.log(result, typeof result.now, result.now instanceof Date);
    const two = await step.run('second', () => {
      return { later: new Date() };
    });
    return {
      message: `Hello ${result.now} ${two.later}!`,
    };
  }
);

superjson-middleware.js

import { InngestMiddleware } from 'inngest';
import superjson from 'superjson';

export const superjsonMiddleware = new InngestMiddleware({
  name: 'Superjson',
  init() {
    return {
      onFunctionRun() {
        return {
          transformInput({ steps }) {
            // Transform steps from Superjson to objects
            const deserializedSteps = steps.map((step) => {
              return {
                ...step,
                data: superjson.deserialize(step.data),
              };
            });
            return {
              steps: deserializedSteps,
            };
          },
          transformOutput({ result, step }) {
            return {
              result: {
                data: superjson.serialize(result.data)
              },
            };
          },
        };
      },
    };
  },
});