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Version: v3

Getting Started

Starting a New Project​

Prerequisites​

Stencil requires a recent LTS version of NodeJS and npm/yarn. Make sure you've installed and/or updated Node before continuing.

Running the create-stencil CLI​

The create-stencil CLI can be used to scaffold a new Stencil project, and can be run using the following command:

 npm init stencil

Stencil can be used to create standalone components, or entire apps. create-stencil, will provide a prompt so that you can choose the type of project to start:

? Select a starter project.

Starters marked as [community] are developed by the Stencil
Community, rather than Ionic. For more information on the 
Stencil Community, please see github.com/stencil-community

❯   component                Collection of web components that can be
                             used anywhere
    app [community]          Minimal starter for building a Stencil 
                             app or website
    ionic-pwa [community]    Ionic PWA starter with tabs layout and routes

Selecting the 'component' option will prompt you for the name of your project. Here, we'll name our project 'my-first-stencil-project':

✔ Pick a starter › component
? Project name › my-first-stencil-project

After hitting ENTER to confirm your choices, the CLI will scaffold a Stencil project for us in a directory that matches the provided project name. Upon successfully creating our project, the CLI will print something similar to the following to the console:

✔ Project name › my-first-stencil-project
✔ A new git repo was initialized
✔ All setup  in 26 ms

  We suggest that you begin by typing:

  $ cd my-first-stencil-project
  $ npm install
  $ npm start

  $ npm start
    Starts the development server.

  $ npm run build
    Builds your project in production mode.

  $ npm test
    Starts the test runner.

  Further reading:

   - https://github.com/ionic-team/stencil-component-starter

  Happy coding! 🎈

The first section describes a few commands required to finish getting your project bootstrapped.

cd my-first-stencil-project
npm install
npm start

This will change your current directory to my-first-stencil-project, install your dependencies for you, and start the development server.

Useful Initial Commands​

The second section of the create-stencil output describes a few useful commands available during the development process:

  • npm start starts a local development server. The development server will open a new browser tab containing your project's components. The dev-server uses hot-module reloading to update your components in the browser as you modify them for a rapid feedback cycle.

  • npm run build creates a production-ready version of your components. The components generated in this step are not meant to be used in the local development server, but rather within a project that consumes your components.

  • npm test runs your project's tests. The create-stencil CLI has created both end-to-end and unit tests when scaffolding your project.

Source Control​

As of create-stencil v3.3.0, a new git repository will be automatically created for you when you initialize a project if:

  1. git is installed
  2. Your project is not created under another git work tree (e.g. if you create a new project in a monorepo, a new git repo will not be created)

Versions of create-stencil prior to v3.3.0 do not interact with any version control systems (VCS). If you wish to place your project under version control, we recommend initializing your VCS now. If you wish to use git, run the following after changing your current directory to the root of your Stencil project:

$ git init
$ git add -A
$ git commit -m "initialize project using stencil cli"

My First Component​

Stencil components are created by adding a new file with a .tsx extension, such as my-component.tsx. The .tsx extension is required since Stencil components are built using JSX and TypeScript.

When we ran create-stencil above, it generated a component, my-component.tsx, that can be found in the src/components/my-component directory:

my-component.tsx
import { Component, Prop, h } from '@stencil/core';
import { format } from '../../utils/utils';

@Component({
  tag: 'my-component',
  styleUrl: 'my-component.css',
  shadow: true,
})
export class MyComponent {
  @Prop() first: string;
  @Prop() middle: string;
  @Prop() last: string;

  private getText(): string {
    return format(this.first, this.middle, this.last);
  }

  render() {
    return <div>Hello, World! I'm {this.getText()}</div>;
  }
}

Once compiled, this component can be used in HTML just like any other tag.

<my-component first="Stencil" middle="'Don't call me a framework'" last="JS"></my-component>

When rendered, the browser will display Hello World! I'm Stencil 'Don't call me a framework' JS.

Anatomy of my-component​

Let's dive in and describe what's happening in my-component, line-by-line.

After the import statements, the first piece we see is the @Component decorator:

@Component({
  tag: 'my-component',
  styleUrl: 'my-component.css',
  shadow: true,
})

This decorator provides metadata about our component to the Stencil compiler. Information, such as the custom element name (tag) to use, can be set here. This decorator tells Stencil to:

Below the @Component() decorator, we have a standard JavaScript class declaration:

export class MyComponent {

Within this class is where you'll write the bulk of your code to bring your Stencil component to life.

Next, the component contains three class members, first, middle and last. Each of these class members have the @Prop() decorator applied to them:

  @Prop() first: string;
  @Prop() middle: string;
  @Prop() last: string;

@Prop() tells Stencil that the property is public to the component, and allows Stencil to rerender when any of these public properties change. We'll see how this works after discussing the render() function.

In order for the component to render something to the screen, we must declare a render() function that returns JSX. If you're not sure what JSX is, be sure to reference the Using JSX docs.

The quick idea is that our render function needs to return a representation of the HTML we want to push to the DOM.

  private getText(): string {
    return format(this.first, this.middle, this.last);
  }
  
  render() {
    return <div>Hello, World! I'm {this.getText()}</div>;
  }

This component's render() returns a <div> element, containing text to render to the screen.

The render() function uses all three class members decorated with @Prop(), through the getText function. Declaring private functions like getText helps pull logic out of the render() function's JSX.

Any property decorated with @Prop() is also automatically watched for changes. If a user of our component were to change the element's first, middle, or last properties, our component would fire its render() function again, updating the displayed content.

Component Generator​

The create-stencil CLI can generate new components for you. If you used one of the starters, you can simply run the generate npm script in your project, which will start the interactive generator.

npm run generate

You can invoke the Stencil CLI directly with the generate command (g for short).

stencil generate
# or
stencil g

If you would like to run stencil generate outside of a Stencil project, it can be installed globally. To do so, prefix the command above with npx, like so:

npx stencil generate

Running a command prefixed with npx will fetch the package for you automatically and prompt you to install it. Once installed, Stencil will run the task to scaffold a new component.

You can optionally pass the component tag name directly to the command. The component tag name needs to be lowercase and contain at least one dash ('-').

stencil generate my-new-component

The generator will ask you which files to generate. This allows you to bootstrap a stylesheet as well as spec and e2e tests along with the component file.

All components will be generated within the src/components folder. Within that directory, a folder will be created with the same name as the component tag name you provided, and within that folder the files will be generated. It is also possible to specify one or multiple sub-folders to generate the component in.

For example, if you specify pages/page-home as the component tag name, the files will be generated in src/components/pages/page-home.

stencil generate pages/page-home
src
└── components
    └── pages
        └── page-home
            ├── page-home.css
            ├── page-home.e2e.ts
            ├── page-home.spec.ts
            └── page-home.tsx

Updating Stencil​

To get the latest version of @stencil/core you can run:

npm install @stencil/core@latest --save-exact

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