Turn TypeScript SDKs Into Temporal Activities

Temporal Activities must be functions, so we can’t easily pass around SDKs like we are used to. I was manually creating function wrappers over each SDK method until Roey Berman from the Temporal team helped me with this function that turned SDKs into Activities.

Here’s an example using the Lago SDK and the Stripe SDK, starting from the Temporal TypeScript dependency injection example:

import type { Api } from "lago-javascript-client";
import type Stripe from "stripe";

// Add prefix to object key https://stackoverflow.com/a/70387184/4717424
type AddPrefixToObject<T, P extends string> = {
  [K in keyof T as K extends string ? `${P}${K}` : never]: T[K];
};

// Get all object keys where values are type V https://stackoverflow.com/a/56874389/4717424
type KeysMatching<T extends object, V> = {
  [K in keyof T]-?: T[K] extends V ? K : never;
}[keyof T];

// SDK after processing
type ProcessedSdk<T extends object, Prefix extends string> = AddPrefixToObject<
  Pick<T, KeysMatching<T, Function>>,
  Prefix
>;

/**
 * Get all functions from SDK, add prefix to key, bind them, and return new object
 */
function turnSdkToObject<T extends object, Prefix extends string>(
  sdkObj: T,
  prefix: Prefix,
  type: "object" | "class"
) {
  if (type === "object") {
    return Object.fromEntries(
      Object.entries(sdkObj)
        .filter(([, v]) => typeof v === "function")
        .map(([name, method]: [string, Function]) => [
          `${prefix}${name}`,
          method.bind(sdkObj),
        ])
    ) as ProcessedSdk<T, Prefix>;
  }
  // If SDK is class https://stackoverflow.com/a/52592900/4717424
  return Object.getOwnPropertyNames(Object.getPrototypeOf(sdkObj))
    .filter(
      (name) =>
        name !== "constructor" && typeof (sdkObj as any)[name] === "function"
    )
    .reduce((methodCollection, methodName) => {
      (methodCollection as any)[`${prefix}${methodName}`] = (sdkObj as any)[
        methodName
      ].bind(sdkObj);
      return methodCollection;
    }, {} as ProcessedSdk<T, Prefix>);
}

export const createActivities = ({
  lagoSDK,
  stripeSDK,
}: {
  lagoSDK: Api<unknown>;
  stripeSDK: Stripe;
}) => ({
  ...turnSdkToObject(stripeSDK.customers, "stripe_customers_", "class"),
  ...turnSdkToObject(lagoClient.customers, "lago_customers_", "object"),
});

We add a prefix in case SDKs have overlapping method names. Now we can use SDKs in our Temporal Activities with minimal manual work.

const { stripe_customers_create, lago_customers_createCustomer } =
  proxyActivities<ReturnType<typeof createActivities>>({
    startToCloseTimeout: "1 minute",
  });