Get the Message notification from Nodejs REST API using Angular8 in background - node.js

Question

I am working on an application where I want to implement the message Inbox. I have created the message inbox using Angular8 and NodeJS REST API. Now I want to get the on inbox message in every 30 Second on the background when user login also it doesn't want to affecting the performance of the Angular app.
So I want to Implement the Web-worker with Angular8 to get the Data from NodeJS REST API but I am unable to create.
I have added following code in Angular 8 App
Add this code to app.component.ts
getWorker(token){
if (typeof Worker !== 'undefined') {
// Create a new
const worker = new Worker('../../web-worker/messenger.worker', { type: `module` });
worker.postMessage(token);
worker.onmessage = (e) => {
setTimeout(() => {
worker.postMessage(token)
}, 15000);
};
} else {
// Web Workers are not supported in this environment.
// You should add a fallback so that your program still executes correctly.
}
}
Created worker file with fetch
/// <reference lib="webworker" />
addEventListener('message', ({ data }) => {
const response = `worker response to ${data}`;
postMessage(response);
});
import { environment } from "src/environments/environment";
onmessage = (message:any) => {
fetch(environment.apiUrl +'messages/notification/1/1',
{ method:'GET',
headers:new Headers({
Authorization: `Bearer ${message.data}`
})
}
)
.then(response => {
return response.json()
})
.then(commits => {
// self.onmessage(message)
return commits
});
};
but it shows the type as fetch is should be show web worker Right?
Can anyone help me with this?