I try out example that go office show about http2 push, but i never work

Getting Help
1

the code goes like following

func main() {
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        pusher, ok := w.(http.Pusher)
        if ok {
            // Push the resource to the client
            if err := pusher.Push("/styles.css", nil); err != nil {
                log.Printf("Failed to push: %v", err)
            }
            if err := pusher.Push("/app.js", nil); err != nil {
                log.Printf("Failed to push: %v", err)
            }
        }

        // Return HTML response
        w.Header().Set("Content-Type", "text/html; charset=utf-8")
        fmt.Fprintf(w, "<html><head><title>HTTP/2 Push Example</title><link rel=\"stylesheet\" href=\"/styles.css\"><script src=\"/app.js\"></script></head><body><h1>Hello, HTTP/2 Push!</h1></body></html>")
    })

    log.Println("HTTP server listening on :8080")
    log.Fatal(http.ListenAndServeTLS(":8080", "server.crt", "server.key", nil))
}

And the app.js is console.log("Hello http2!")

But when I use chrome to visit https://localhost:8080
what was shown in the app.js file is something like following:
<html><head><title>HTTP/2 Push Example</title><link rel=\"stylesheet\" href=\"/styles.css\"><script src=\"/app.js\"></script></head><body><h1>Hello, HTTP/2 Push!</h1></body></html>

So what’s going on?

And more interesting, if I just use the gin’s example of http2 push, it just work as it should be.