JS如何实现一个单文件组件

<template>
  <!-- Button.html contents Go here. -->
</template>

<style>
  
</style>

<script>
  // Button.js contents go here.
</script>

window.loadComponent = (function() {
  function loadComponent( URL ) {}
  return loadComponent;
}());

<template>
  <div class="hello">
    <p>Hello, world! My name is <slot></slot>.</p>
  </div>
</template>
<style>
  div {
    background: red;
    border-radius: 30px;
    padding: 20px;
    font-size: 20px;
    text-align: center;
    width: 300px;
    margin: 0 auto;
  }
</style>
<script></script>

<hello-world>Comandeer</hello-world>
<script src="loader.js"></script>
<script>
  loadComponent( 'HelloWorld.wc' );
</script>

function loadComponent( URL ) {
  return fetch( URL );
}

function loadComponent( URL ) {
  return fetch( URL ).then( ( response ) => {
    return response.text();
  } );
}

loadComponent('HelloWorld.wc').then((component) => {
    console.log(component);
});

window.loadComponent = (function () {
    function loadComponent(URL) {
        return fetch(URL).then((response) => {
            return response.text();
        }).then((html) => {
            const parser = new DOMParser(); // 1
            return parser.parseFromString(html, 'text/html'); // 2
        });
    }
    return loadComponent;
}());

return fetch(URL).then((response) => {
    return response.text();
}).then((html) => {
    const parser = new DOMParser();
    const document = parser.parseFromString(html, 'text/html');
    const head = document.head;
    const template = head.querySelector('template');
    const style = head.querySelector('style');
    const script = head.querySelector('script');

    return {
        template,
        style,
        script
    };
}); 

window.loadComponent = (function () {
    function fetchAndParse(URL) {
        return fetch(URL).then((response) => {
            return response.text();
        }).then((html) => {
            const parser = new DOMParser();
            const document = parser.parseFromString(html, 'text/html');
            const head = document.head;
            const template = head.querySelector('template');
            const style = head.querySelector('style');
            const script = head.querySelector('script');

            return {
                template,
                style,
                script
            };
        });
    }

    function loadComponent(URL) {
        return fetchAndParse(URL);
    }

    return loadComponent;
}()); 

window.loadComponent = (function () {
    function fetchAndParse(URL) {
        […]
    }
    function registerComponent() {
    }
    function loadComponent(URL) {
        return fetchAndParse(URL).then(registerComponent);
    }
    return loadComponent;
}()); 

function registerComponent({template, style, script}) {
    class UnityComponent extends HTMLElement {
        connectedCallback() {
            this._upcast();
        }

        _upcast() {
            const shadow = this.attachShadow({mode: 'open'});
            shadow.appendChild(style.clonenode(true));
            shadow.appendChild(document.importNode(template.content, true));
        }
    }
} 

function registerComponent( { template, style, script } ) {
  class UnityComponent extends HTMLElement {
    [...]
  }

  return customElements.define( 'hello-world', UnityComponent );
} 

<template>
  […]
</template>

<style>
  […]
</style>

<script>
  export default { // 1
    name: 'hello-world', // 2
    onClick() { // 3
      alert( `Don't touch me!` );
    }
  }
</script> 

export default true; 

data:application/javascript;base64,ZXhwb3J0IGRlZmF1bHQgdHJ1ZTs= 

import test from 'data:application/javascript;base64,ZXhwb3J0IGRlZmF1bHQgdHJ1ZTs=';
console.log( test ); 

const myJSFile = new Blob( [ 'export default true;' ], { type: 'application/javascript' } );
const myJSURL = URL.createObjectURL( myJSFile );

console.log( myJSURL ); // blob:https://blog.comandeer.pl/8e8fbd73-5505-470d-a797-dfb06ca71333 

const myJSFile = new Blob( [ 'export default true;' ], { type: 'application/javascript' } );
const myJSURL = URL.createObjectURL( myJSFile );

import( myJSURL ).then( ( module ) => {
  console.log( module.default ); // true
}); 

function getSettings( { template, style, script } ) {
  return {
    template,
    style,
    script
  };
}
[...]
function loadComponent( URL ) {
  return fetchAndParse( URL ).then( getSettings ).then( registerComponent );
} 

const jsFile = new Blob( [ script.textContent ], { type: 'application/javascript' } );
const jsURL = URL.createObjectURL( jsFile ); 

return import( jsURL ).then( ( module ) => {
  return {
    name: module.default.name,
    template,
    style
  }
} ); 

function registerComponent( { template, style, name } ) {
  class UnityComponent extends HTMLElement {
    [...]
  }

  return customElements.define( name, UnityComponent );
} 

function getSettings( { template, style, script } ) {
  [...]

  function getListeners( settings ) { // 1
    const listeners = {};

    Object.entries( settings ).forEach( ( [ setting, value ] ) => { // 3
      if ( setting.startsWith( 'on' ) ) { // 4
        listeners[ setting[ 2 ].toLowerCase() + setting.substr( 3 ) ] = value; // 5
      }
    } );

    return listeners;
  }

  return import( jsURL ).then( ( module ) => {
    const listeners = getListeners( module.default ); // 2

    return {
      name: module.default.name,
      listeners, // 6
      template,
      style
    }
  } );
} 

function getListeners( settings ) {
  return Object.entries( settings ).reduce( ( listeners, [ setting, value ] ) => {
    if ( setting.startsWith( 'on' ) ) {
      listeners[ setting[ 2 ].toLowerCase() + setting.substr( 3 ) ] = value;
    }

    return listeners;
  }, {} );
} 

function registerComponent( { template, style, name, listeners } ) { // 1
  class UnityComponent extends HTMLElement {
    connectedCallback() {
      this._upcast();
      this._attachListeners(); // 2
    }
    [...]
    _attachListeners() {
      Object.entries( listeners ).forEach( ( [ event, listener ] ) => { // 3
        this.addEventListener( event, listener, false ); // 4
      } );
    }
  }
  return customElements.define( name, UnityComponent );
}