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Version: v4.0

Angular Integration

Supports: Angular 12+ • TypeScript 4.0+ • Stencil v2.9.0+

Stencil can generate Angular component wrappers for your web components. This allows your Stencil components to be used within an Angular application. The benefits of using Stencil's component wrappers over the standard web components include:

  • Angular component wrappers will be detached from change detection, preventing unnecessary repaints of your web component.
  • Web component events will be converted to RxJS observables to align with Angular's @Output() and will not emit across component boundaries.
  • Optionally, form control web components can be used as control value accessors with Angular's reactive forms or [ngModel].
  • It is not necessary to include the Angular CUSTOM_ELEMENTS_SCHEMA in all modules consuming your Stencil components.

Setup​

Project Structure​

We recommend using a monorepo structure for your component library with component wrappers. Your project workspace should contain your Stencil component library and the library for the generated Angular component wrappers.

An example project set-up may look similar to:

top-most-directory/
└── packages
    ├── stencil-library/
    │   ├── stencil.config.js
    │   └── src/components
    └── angular-workspace/
        └── projects/
            └── component-library/
                └── src/
                    ├── lib/
                    └── public-api.ts

This guide uses Lerna for the monorepo, but you can use other solutions such as Nx, Turborepo, etc.

To use Lerna with this walk through, globally install Lerna:

npm install --global lerna

Creating a Monorepo​

note

If you already have a monorepo, skip this section.

# From your top-most-directory/, initialize a workspace
lerna init

# install dependencies
npm install

# install typescript and node types
npm install typescript @types/node --save-dev

Creating a Stencil Component Library​

note

If you already have a Stencil component library, skip this section.

In the packages/ directory, run the following commands to generate a Stencil component library:

npm init stencil components stencil-library
cd stencil-library
# Install dependencies
npm install

Creating an Angular Component Library​

note

If you already have an Angular component library, skip this section.

The first time you want to create the component wrappers, you will need to have an Angular library package to write to.

In the packages/ directory, use the Angular CLI to generate a workspace and a library for your Angular component wrappers:

npx -p @angular/cli ng new angular-workspace --no-create-application
cd angular-workspace
npx -p @angular/cli ng generate library component-library

You can delete the component-library.component.ts, component-library.service.ts, and *.spec.ts files.

You will also need to add your generated Stencil library as a peer-dependency so import references can be resolved correctly:

// packages/angular-workspace/projects/component-library/package.json

"peerDependencies": {
   "@angular/common": "^15.1.0",
-  "@angular/core": "^15.1.0"
+  "@angular/core": "^15.1.0",
+  "stencil-library": "*"
}

For more information, see the Lerna documentation on package dependency management.

note

The Angular CLI will install Jasmine as a dependency to your Angular workspace. However, Stencil uses Jest as it's unit testing solution. To avoid type definition collisions when attempting to build your Stencil project, you can remove jasmine-core and @types/jasmine as dependencies in the Angular workspace package.json file:

# from `/packages/angular-workspace`
npm uninstall jasmine-core @types/jasmine

Adding the Angular Output Target​

Install the @stencil/angular-output-target dependency to your Stencil component library package.

# Install dependency
npm install @stencil/angular-output-target --save-dev

In your project's stencil.config.ts, add the angularOutputTarget configuration to the outputTargets array:

import { angularOutputTarget } from '@stencil/angular-output-target';

export const config: Config = {
  namespace: 'stencil-library',
  outputTargets: [
    // By default, the generated proxy components will
    // leverage the output from the `dist` target, so we
    // need to explicitly define that output alongside the
    // Angular target
    {
      type: 'dist',
    },
    angularOutputTarget({
      componentCorePackage: 'stencil-library',
      outputType: 'component',
      directivesProxyFile: '../angular-workspace/projects/component-library/src/lib/stencil-generated/components.ts',
      directivesArrayFile: '../angular-workspace/projects/component-library/src/lib/stencil-generated/index.ts',
    }),
  ],
};
tip

The componentCorePackage should match the name field in your Stencil project's package.json.

outputType should be set to 'component' for Stencil projects using the dist output. Otherwise if using the custom elements output, outputType should be set to 'scam' or 'standalone'.

The directivesProxyFile is the relative path to the file that will be generated with all of the Angular component wrappers. You will replace the file path to match your project's structure and respective names. You can generate any file name instead of components.ts.

The directivesArrayFile is the relative path to the file that will be generated with a constant of all the Angular component wrappers. This constant can be used to easily declare and export all the wrappers.

See the API section below for details on each of the output target's options.

You can now build your Stencil component library to generate the component wrappers.

# Build the library and wrappers
npm run build

If the build is successful, you will now have contents in the file specified in directivesProxyFile and directivesArrayFile.

You can now finally import and export the generated component wrappers for your component library. For example, in your library's main Angular module:

// component-library.module.ts

import { DIRECTIVES } from './stencil-generated';

@NgModule({
  declarations: [...DIRECTIVES],
  exports: [...DIRECTIVES],
})
export class ComponentLibraryModule {}

Any components that are included in the exports array should additionally be exported in your main entry point (either public-api.ts or index.ts). Skipping this step will lead to Angular Ivy errors when building for production. For this guide, simply add the following line to the automatically generated public-api.ts file:

// public-api.ts

export * from './lib/component-library.module';
export { DIRECTIVES } from './lib/stencil-generated';
export * from './lib/stencil-generated/components';

Registering Custom Elements​

The default behavior for this output target does not handle automatically defining/registering the custom elements. One strategy (and the approach the Ionic Framework takes) is to use the loader to define all custom elements during app initialization:

// component-library.module.ts

import { APP_INITIALIZER, NgModule } from '@angular/core';
import { defineCustomElements } from 'stencil-library/loader';

@NgModule({
  ...,
  providers: [
    {
      provide: APP_INITIALIZER,
      useFactory: () => defineCustomElements,
      multi: true
    },
  ]
})
export class ComponentLibraryModule {}

See the documentation for more information on defining custom elements using the dist output target, or update the Angular output target to use dist-custom-elements.

note

If you are using a monorepo tool (Lerna, Nx, etc.), skip this section.

Before you can successfully build a local version of your Angular component library, you will need to link the Stencil package to the Angular package.

From your Stencil project's directory, run the following command:

# Link the working directory
npm link

From your Angular component library's directory, run the following command:

# Link the package name
npm link name-of-your-stencil-package

The name of your Stencil package should match the name property from the Stencil component library's package.json.

Your component libraries are now linked together. You can make changes in the Stencil component library and run npm run build to propagate the changes to the Angular component library.

note

As an alternative to npm link , you can also run npm install with a relative path to your Stencil component library. This strategy, however, will modify your package.json so it is important to make sure you do not commit those changes.

Consumer Usage​

Creating a Consumer Angular App​

note

If you already have an Angular app, skip this section.

From your Angular workspace (/packages/angular-workspace), run the following command to generate an Angular application:

npx -p @angular/cli ng generate app my-app

Consuming the Angular Wrapper Components​

This section covers how developers consuming your Angular component wrappers will use your package and component wrappers.

In order to use the generated component wrappers in the Angular app, you'll first need to build your Angular component library. From the root of your Angular workspace (/packages/angular-workspace), run the following command:

npx -p @angular/cli ng build component-library
note

In the output of the ng build command you may see a warning that looks like this:

▲ [WARNING] The glob pattern import("./**/.entry.js") did not match any files [empty-glob]

node_modules/@stencil/core/internal/client/index.js:3808:2:
  3808 │   `./${bundleId}.entry.js${BUILD.hotModuleReplacement && hmrVers...
       ╵   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is a known issue in esbuild (used under the hood by ng build) and should not cause an issue, but at present there's unfortunately no way to suppress this warning.

Now you can reference your component library as a standard import. If you distributed your components through a primary NgModule, you can simply import that module into an implementation to use your components.

// app.module.ts

import { ComponentLibraryModule } from 'component-library';

@NgModule({
  imports: [ComponentLibraryModule],
})
export class AppModule {}

You can now directly leverage your components in their template and take advantage of Angular template binding syntax.

<!-- app.component.html -->

<my-component first="Your" last="Name"></my-component>

From your Angular workspace (/packages/angular-workspace), run npm start and navigate to localhost:4200. You should see the component rendered correctly.

API​

componentCorePackage​

Required

Type: string

The name of the Stencil package where components are available for consumers (i.e. the value of the name property in your Stencil component library's package.json). This is used during compilation to write the correct imports for components.

For a starter Stencil project generated by running:

npm init stencil component my-component-lib

The componentCorePackage would be set to:

// stencil.config.ts

export const config: Config = {
  ...,
  outputTargets: [
    angularOutputTarget({
      componentCorePackage: 'my-component-lib',
      // ... additional config options
    })
  ]
}

Which would result in an import path like:

import { MyComponent } from 'my-component-lib/components/my-component.js';

customElementsDir​

Optional

Default: 'components'

Type: string

This option can be used to specify the directory where the generated custom elements live.

excludeComponents​

Optional

Default: []

Type: string[]

This lets you specify component tag names for which you don't want to generate Angular wrapper components. This is useful if you need to write framework-specific versions of components. For instance, in Ionic Framework, this is used for routing components - like tabs - so that Ionic Framework can integrate better with Angular's Router.

directivesArrayFile​

Optional

Default: null

Type: string

Used to provide a list of type Proxies to the Angular Component Library. See Ionic Framework for a sample.

directivesProxyFile​

Required

Type: string

This parameter allows you to name the file that contains all the component wrapper definitions produced during the compilation process. This is the first file you should import in your Angular project.

outputType​

Required

Default: 'component'

Type: 'component' | 'scam' | 'standalone

Specifies the type of output to be generated. It can take one of the following values:

  1. component: Generates all the component wrappers to be declared on an Angular module. This option is required for Stencil projects using the dist hydrated output.

  2. scam: Generates a separate Angular module for each component.

  3. standalone: Generates standalone component wrappers.

Both scam and standalone options are compatible with the dist-custom-elements output.

Note: Please choose the appropriate outputType based on your project's requirements and the desired output structure.

valueAccessorConfigs​

Optional

Default: []

Type: ValueAccessorConfig[]

This lets you define which components should be integrated with ngModel (i.e. form components). It lets you set what the target prop is (i.e. value), which event will cause the target prop to change, and more.

const angularValueAccessorBindings: ValueAccessorConfig[] = [
  {
    elementSelectors: ['my-input[type=text]'],
    event: 'myChange',
    targetAttr: 'value',
    type: 'text',
  },
];

export const config: Config = {
  namespace: 'stencil-library',
  outputTargets: [
    angularOutputTarget({
      componentCorePackage: 'component-library',
      directivesProxyFile: '{path to your proxy file}',
      valueAccessorConfigs: angularValueAccessorBindings,
    }),
    {
      type: 'dist',
      esmLoaderPath: '../loader',
    },
  ],
};

FAQs​

Do I have to use the dist output target?​

No! By default, this output target will look to use the dist output, but the output from dist-custom-elements can be used alternatively.

To do so, simply set the includeImportCustomElements option in the output target's config and ensure the custom elements output target is added to the Stencil config's output target array:

// stencil.config.ts

export const config: Config = {
  ...,
  outputTargets: [
    // Needs to be included
    {
      type: 'dist-custom-elements'
    },
    angularOutputTarget({
      componentCorePackage: 'component-library',
      directivesProxyFile: '{path to your proxy file}',
      // This is what tells the target to use the custom elements output
      includeImportCustomElements: true
    })
  ]
}

Now, all generated imports will point to the default directory for the custom elements output. If you specified a different directory using the dir property for dist-custom-elements, you need to also specify that directory for the Angular output target. See the API section for more information.

In addition, all the Web Component will be automatically defined as the generated component modules are bootstrapped. So, you do not need to implement the Stencil loader for lazy-loading the custom elements (i.e. you can remove the APP_INITIALIZER logic introduced in this section). As such, the generated Angular components can now be directly imported and declared on any Angular module implementing them:

// app.module.ts

import { MyComponent } from 'component-library';

@NgModule({
  declarations: [MyComponent],
})
export class AppModule {}

What is the best format to write event names?​

Event names shouldn’t include special characters when initially written in Stencil, try to lean on using camelCased event names for interoperability between frameworks.

How do I bind input events directly to a value accessor?​

You can configure how your input events can map directly to a value accessor, allowing two-way data-binding to be a built in feature of any of your components. Take a look at valueAccessorConfig's option above.

How do I access components with ViewChild or ViewChildren?​

Once included, components could be referenced in your code using ViewChild and ViewChildren as in the following example:

import { Component, ElementRef, ViewChild } from '@angular/core';

import { TestComponent } from 'test-components';

@Component({
  selector: 'app-home',
  template: `<test-components #test></test-components>`,
  styleUrls: ['./home.component.scss'],
})
export class HomeComponent {
  @ViewChild(TestComponent) myTestComponent: ElementRef<TestComponent>;

  async onAction() {
    await this.myTestComponent.nativeElement.testComponentMethod();
  }
}

Why aren't my custom interfaces exported from within the index.d.ts file?​

Usually when beginning this process, you may bump into a situation where you find that some of the interfaces you've used in your Stencil component library aren't working in your Angular component library. You can resolve this issue by adding an interfaces.d.ts file located within the root of your Stencil component library's project folder, then manually exporting types from that file e.g. export * from './components';

When adding this file, it's also recommended to update your package.json's types property to be the distributed file, something like: "types": "dist/types/interfaces.d.ts"

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