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My First Component

Stencil components are created by adding a new file with a .tsx extension, such as my-first-component.tsx, and placing them in the src/components directory. The .tsx extension is required since Stencil components are built using JSX and TypeScript.

Here is an example of what a Stencil component looks like:

import { Component, Prop, h } from '@stencil/core';

@Component({
  tag: 'my-first-component',
})
export class MyComponent {

  // Indicate that name should be a public property on the component
  @Prop() name: string;

  render() {
    return (
      <p>
        My name is {this.name}
      </p>
    );
  }
}

Don't fully understand what's going on? Don't worry, we'll explain each piece in detail later on.

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

<my-first-component name="Max"></my-first-component>

Web Components must have a - in the tag. firstComponent would not be a valid tag name.

When rendered, the browser will display My name is Max.

So what is really going on here?

Let's dive in.

The first piece we see is the @Component decorator. This decorator provides metadata about our component to the Stencil compiler. Information, such as the tag to use, and external styles, can be set here and picked up by the compiler.

Below the @Component() decorator, we have a standard JavaScript class. This is where you'll write the bulk of your code to bring your Stencil component to life. Here is where you'd write functions or provide business logic.

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, don't worry, we'll go over it in detail in the Templating Docs.

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

The name property on the class also has a decorator applied to it, @Prop(). This decorator tells the compiler that the property is public to the component, and the user should be setting it. We set this property like so:

<my-first-component name="Max"></my-first-component>

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

Component Generator

The 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

Or you can invoke the Stencil CLI directly with the generate command (g for short). If you don't have stencil installed globally, prefix the command with npx.

stencil generate

You can optionally pass the component tag name directly to the command. Remember that the component tag name needs to be lowercase and contain at least one hyphen. In the second step, 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, 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
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