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Nx Devkit and Angular Devkit

Nx comes with a devkit to write generators and executors, but you can also use Angular devkit (schematics and builders). An Angular schematic is a second way to implement generators. An Angular builder is a second way to implement an executor.

What is the difference between Nx Devkit and Angular Devkit?

Generators

The following is a generator written using Nx Devkit:

import { Tree, formatFiles, generateFiles } from '@nrwl/devkit';
import * as path from 'path';

interface Schema {
  name: string;
  skipFormat: boolean;
}

export default async function (host: Tree, optoins: Schema) {
  generateFiles(
    host,
    path.join(__dirname, 'files'),
    path.join('tools/generators', schema.name),
    options
  );
  if (!schema.skipFormat) {
    await formatFiles(host);
  }
}

The following is an analogous generator written as an Angular Schematic.

import {
  apply,
  branchAndMerge,
  chain,
  mergeWith,
  Rule,
  template,
  url,
  move,
} from '@angular-devkit/schematics';
import { formatFiles } from '@nrwl/workspace';
import { toFileName } from '@nrwl/workspace';

interface Schema {
  name: string;
  skipFormat: boolean;
}

export default function (options: Schema): Rule {
  const templateSource = apply(url('./files'), [
    template({
      dot: '.',
      tmpl: '',
      ...(options as any),
    }),
    move('tools/generators'),
  ]);
  return chain([
    branchAndMerge(chain([mergeWith(templateSource)])),
    formatFiles(options),
  ]);
}

Some notable changes:

  • Nx Devkit generators do not use partial application. An Angular Schematic returns a rule that is then invoked with a host.
  • Nx Devkit generators do not use chain. Just invoke the helpers directly. This makes them more debuggable. As you step through the generator you can see the host being updated.
  • chain([mergeWith(apply(url is replaced with generateFiles :)
  • Nx Devkit generators return a function that performs side effects. Angular Schematics have to create a custom task runner and register a task using it.
  • You don't need any special helpers to compose Nx Devkit generators. You do need to go through a special resolution step to compose schematics.
  • No special utilities needed to test Nx Devkit generators. Special utilities are needed to test Angular Schematics.

The schema files for both Nx Devkit generators and Angular Schematics are the same. Nx can run both of them in the same way. You can invoke Angular schematics from withing Nx Devkit generator using wrapAngularDevkitSchematic.

Executors

The following is an executor written using Nx Devkit:

interface Schema {
  message: string;
  allCaps: boolean;
}

export default async function (
  options: Schema,
  context: TargetContext
): Promise<{ success: true }> {
  if (options.allCaps) {
    console.log(options.message.toUpperCase());
  } else {
    console.log(options.message);
  }
  return { success: true };
}

Same executor written as an Angular builder:

interface Schema {
  message: string;
  allCaps: boolean;
}

export default function (
  options: Schema,
  context: BuilderContext
): Observable<{ success: true }> {
  if (options.allCaps) {
    console.log(options.message.toUpperCase());
  } else {
    console.log(options.message);
  }
  return of({ success: true });
}
export default createBuilder<NextBuildBuilderOptions>(run);

Some notable changes:

  • Nx Devkit executors return promises. If you want, you can always convert an observable to a promise.
  • Nx Devkit executors do not have to be wrapped using createBuilder.

The schema files for both Nx Devkit executors and Angular Builders are the same. Nx can run both of them in the same way.

When to Use What

If you are writing an Nx plugin, use Nx Devkit. It's easier to use, easier to debug. If you are writing a plugin that can be used in an Nx workspace or in a regular Angular CLI project, use Angular Devkit.

The end user might not even know what you used to write a generator or an executor. The examples above will work the same way.