index.html

<html>
  <head>
    <title>Demo of element-lite</title>
  </head>
  <body>
    <test-component></test-component>
    <script type="module">
      import { ElementLiteBase } from './element-lite-base.js';

      class TestComponent extends ElementLiteBase(window.HTMLElement) {
        static get is () { return 'test-component'; }

        static get properties () {
          return {
            prop1: {
              type: String,
              value: 'Hello',
              observer: '_testMethod'
            },
            prop2: {
              type: String,
              value: 'World',
              observer: '_testMethod'
            }
          };
        }

        static get observers () {
          return [
            '_testTwoProps(prop1, prop2)',
            '_testTwoProps(prop2, prop1)'
          ];
        }

        _testMethod (prop1) {
          console.log(prop1);
        }

        _testTwoProps (prop1, prop2) {
          console.log(prop1, prop2);
        }
      }

      window.customElements.define(TestComponent.is, TestComponent);
    </script>
  </body>
</html>