handler.go

func (handler *designerHandler) Notify(ctx *fiber.Ctx) error {
	ctx.Set(fiber.HeaderContentType, "text/event-stream")
	ctx.Set(fiber.HeaderCacheControl, "no-cache")
	ctx.Set(fiber.HeaderConnection, "keep-alive")
	ctx.Set(fiber.HeaderTransferEncoding, "chunked")
	ctx.Context().SetBodyStreamWriter(func(w *bufio.Writer) {
		for {
			if handler.q.Length() == 0 {
				time.Sleep(time.Second * 1)
				continue
			}
			handler.mu.Lock()
			item := handler.q.Remove()
			if item == nil {
				log.Printf("ERR_QUEUE: failed to get message\n")
				handler.mu.Unlock()
				return
			}
			if _, err := fmt.Fprintf(w, "data: %s\n\n", *item); err != nil {
				log.Printf("ERR_WRITE: %v\n", err)
				handler.mu.Unlock()
				return
			}
			if err := w.Flush(); err != nil {
				log.Printf("ERR_FLUSH: %v\n", err)
				handler.mu.Unlock()
				return
			}
			handler.mu.Unlock()
		}
	})
	return nil
}

index.js

let sseSource = null;
const apiURL = "http://localhost:3000/designer";
const sseURL = `${apiURL}/notifications`;
const confURL = `${apiURL}/configurations`;

document.addEventListener('DOMContentLoaded', () => {
    if(typeof(EventSource) !== "undefined") {
        sseSource = new EventSource(sseURL);
        sseSource.addEventListener("message", function(event) {
           const data = event.data;
           showNotificationDialog(data);
        });
        sseSource.addEventListener('error', function() {
           if (sseSource.readyState === EventSource.CLOSED) {
               sseSource = new EventSource(sseURL);
           }
       });
    } else {
       alert("Sorry, your browser does not support server-sent events...");
    }
    document.getElementById('copyright').textContent = `
        COPYRIGHT © ${new Date().getFullYear()} SKILLEDIN PTE. LTD. ALL RIGHTS RESERVED.
    `;
});

data, err := cred.GetToken(context.Background(), policy.TokenRequestOptions{
Scopes: []string{"https://graph.microsoft.com/.default"},
})
fmt.Println(data.Token, err)