What is error The script has an unsupported MIME type ('text/html') in vuejs and nodejs when use service worker and web-push

i have some code in vuejs and nodejs to push notification . i use service worker and web-push library.

I have this code in vuejs in help.js file :

  function urlBase64ToUint8Array(base64String) {
    const padding = '='.repeat((4 - base64String.length % 4) % 4);
    const base64 = (base64String + padding)
    .replace(/-/g, '+')
    .replace(/_/g, '/');

    const rawData = window.atob(base64);
    const outputArray = new Uint8Array(rawData.length);

   for (let i = 0; i < rawData.length; ++i) {
      outputArray[i] = rawData.charCodeAt(i);
    }
     return outputArray;
}
  let publicKey =      "BFQls47BpgbbWO44BS85Lk9ekzy7sVOQCXFteZTUwxXwpUQEKaY4hHVuUqjIxwYMStohiqYvPjH4FBctOHDOsHA"
 export let send = async () => {
       try {
      const registration = await navigator.serviceWorker.
       register('./worker.js', {scope: '/'})

    let subscribe = await registration.pushManager.subscribe({
        userVisibleOnly: true,
        applicationServerKey: urlBase64ToUint8Array(publicKey)
    });
    console.log(subscribe);
    await fetch('/subscribe', {
        method: 'POST',
        body:JSON.stringify(subscribe),
        headers: {
          'content-type': 'application/json'
        }
      });
} catch (err) {
    console.log(err);

}

}

and in sendNotification.vue file methods I have this code:

       export default{
       methods : {
       sendNotification() {

        if ("serviceWorker" in navigator) {
            console.log("send");
            send(this.title, this.text);

            // this.socket.emit("sendingNotification",{title:this.title,text:this.text});
        }

       }
  }
}

and when i click on button in sendNotification.vue component sendNotification() method is fire.

this my route in nodejs using express :

     let publicKey = "BFQls47BpgbbWO44BS85Lk9ekzy7sVOQCXFteZTUwxXwpUQEKaY4hHVuUqjIxwYMStohiqYvPjH4FBctOHDOsHA";
      let privateKey = "wVK3KWm77rvYCaivhLXynu8l_DefDA5hBoCqNdExMes";
       webPush.setVapidDetails("mailto:ash.**********@gmail.com", publicKey, privateKey);
 app.post('/subscribe',(req,res)=>{
    let body = req.body;
   console.log(body);
    let payload = JSON.stringify({"title":"hi","text":"welcome "});

     webPush.sendNotification(body, payload).catch(e => console.log(e));
     res.status(201).json(payload);
  });

but i get this error in console :

The script has an unsupported MIME type ('text/html').

help.js?b127:37 DOMException: Failed to register a ServiceWorker for scope ('http://localhost:8080/') with script ('http://localhost:8080/worker.js'): The script has an unsupported MIME type ('text/html').

what is wrong in my code?

and another question, can I use socket.io Instead express?