nx/docs/shared/recipes/plugins/compose-executors.md

title	description
Compose Executors	Learn how to compose and chain Nx executors together, including how to invoke other targets and executors from within your custom executors.

Compose executors

An executor is just a function, so you can import and invoke it directly, as follows:

import printAllCaps from 'print-all-caps';

export default async function (
  options: Schema,
  context: ExecutorContext
): Promise<{ success: true }> {
  // do something before
  await printAllCaps({ message: 'All caps' });
  // do something after
}

This only works when you know what executor you want to invoke. Sometimes, however, you need to invoke a target. For instance, the e2e target is often configured like this:

{
  "e2e": {
    "builder": "@nx/cypress:cypress",
    "options": {
      "cypressConfig": "apps/myapp-e2e/cypress.json",
      "tsConfig": "apps/myapp-e2e/tsconfig.e2e.json",
      "devServerTarget": "myapp:serve"
    }
  }
}

In this case we need to invoke the target configured in devSeverTarget. We can do it as follows:

async function* startDevServer(
  opts: CypressExecutorOptions,
  context: ExecutorContext
) {
  const { project, target, configuration } = parseTargetString(
    opts.devServerTarget
  );
  for await (const output of await runExecutor<{
    success: boolean;
    baseUrl?: string;
  }>(
    { project, target, configuration },
    {
      watch: opts.watch,
    },
    context
  )) {
    if (!output.success && !opts.watch)
      throw new Error('Could not compile application files');
    yield opts.baseUrl || (output.baseUrl as string);
  }
}

The runExecutor utility will find the target in the configuration, find the executor, construct the options (as if you invoked it in the terminal) and invoke the executor. Note that runExecutor always returns an iterable instead of a promise.

Devkit helper functions

Property	Description
logger	Wraps console to add some formatting
getPackageManagerCommand	Returns commands for the package manager used in the workspace
parseTargetString	Parses a target string into {project, target, configuration}
readTargetOptions	Reads and combines options for a given target
runExecutor	Constructs options and invokes an executor

See more helper functions in the Devkit API Docs

Using RxJS observables

The Nx devkit only uses language primitives (promises and async iterables). It doesn't use RxJS observables, but you can use them and convert them to a Promise or an async iterable.

You can convert Observables to a Promise with toPromise.

import { of } from 'rxjs';

export default async function (opts) {
  return of({ success: true }).toPromise();
}

You can use the rxjs-for-await library to convert an Observable into an async iterable.

import { of } from 'rxjs';
import { eachValueFrom } from 'rxjs-for-await';

export default async function (opts) {
  return eachValueFrom(of({ success: true }));
}