98 lines
3.2 KiB
Markdown
98 lines
3.2 KiB
Markdown
# Compose executors
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An executor is just a function, so you can import and invoke it directly, as follows:
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```typescript
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import printAllCaps from 'print-all-caps';
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export default async function (
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options: Schema,
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context: ExecutorContext
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): Promise<{ success: true }> {
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// do something before
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await printAllCaps({ message: 'All caps' });
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// do something after
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}
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```
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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:
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```json {% fileName="project.json" %}
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{
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"e2e": {
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"builder": "@nrwl/cypress:cypress",
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"options": {
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"cypressConfig": "apps/myapp-e2e/cypress.json",
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"tsConfig": "apps/myapp-e2e/tsconfig.e2e.json",
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"devServerTarget": "myapp:serve"
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}
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}
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}
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```
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In this case we need to invoke the target configured in devSeverTarget. We can do it as follows:
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```typescript
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async function* startDevServer(
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opts: CypressExecutorOptions,
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context: ExecutorContext
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) {
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const { project, target, configuration } = parseTargetString(
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opts.devServerTarget
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);
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for await (const output of await runExecutor<{
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success: boolean;
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baseUrl?: string;
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}>(
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{ project, target, configuration },
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{
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watch: opts.watch,
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},
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context
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)) {
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if (!output.success && !opts.watch)
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throw new Error('Could not compile application files');
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yield opts.baseUrl || (output.baseUrl as string);
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}
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}
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```
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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.
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## Devkit helper functions
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| Property | Description |
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| ------------------------ | -------------------------------------------------------------- |
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| logger | Wraps `console` to add some formatting |
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| getPackageManagerCommand | Returns commands for the package manager used in the workspace |
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| parseTargetString | Parses a target string into `{project, target, configuration}` |
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| readTargetOptions | Reads and combines options for a given target |
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| runExecutor | Constructs options and invokes an executor |
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See more helper functions in the [Devkit API Docs](/packages/devkit/documents/nrwl_devkit#functions)
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## Using RxJS observables
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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.
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You can convert `Observables` to a `Promise` with `toPromise`.
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```typescript
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import { of } from 'rxjs';
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export default async function (opts) {
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return of({ success: true }).toPromise();
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}
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```
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You can use the [`rxjs-for-await`](https://www.npmjs.com/package/rxjs-for-await) library to convert an `Observable` into an async iterable.
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```typescript
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import { of } from 'rxjs';
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import { eachValueFrom } from 'rxjs-for-await';
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export default async function (opts) {
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return eachValueFrom(of({ success: true }));
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}
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```
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