index.js

document.addEventListener('DOMContentLoaded', async (e) => {
  let controller = new AbortController();
  document.querySelector('#button').onclick = async (e) => {
    try {
      const signal = controller.signal;
      const result = await fetch('/json', {signal});
      document.querySelector('#result').innerText = JSON.stringify(await result.json()); 
    } catch (e) {
      console.log(e);
      controller = new AbortController();
    }
  }

  document.querySelector('#abort').onclick = async (e) => {
    controller.abort();
    document.querySelector('#result').innerText = '中止しました';
  }
});