使用

  const options {
    withCredentials: true,  // 默认 false
  }

  const eventSource = new EventSource(`/api`, options);

  eventSource.addEventListener('open', () => {});
  eventSource.onmessage = (event) => {};   // 或addEventListener('message',callback)
  eventSource.addEventListener('error', (event) => {});

注意：message 为默认事件

后端可配合前端使用自定义事件

后端配置 content-type="text/event-stream"

参考：https://www.ruanyifeng.com/blog/2017/05/server-sent_events.html