One parameter

<canvas></canvas>
<script src="https://script.layerstatic.com/layer/sdk-latest.js"></script>
<script src="./app.js"></script>
<script>
  const canvas = document.querySelector('canvas');
	
  const app = new App(canvas);

  globalThis.addEventListener('layer:paramchange', (event) => {
	  const { id, value } = event.detail;
	  if (id === 'choice') app.choice = value;
  });

  $layer
    .registerCanvas(canvas)
    .params(
      {
        customization_level: 'VIEWER',
        kind: 'LIST',
        id: 'choice',
        name: 'List',
        default: 'option2',
        options: [
          {
            value: 'option1',
            label: 'Option 1',
          },
          {
            value: 'option2',
            label: 'Option 2',
          },
          {
            value: 'option3',
            label: 'Option 3',
          },
        ],
      }
    ).then(({ choice }) => {
      app.choice = choice;
      app.start();
    });
</script>