How to only allow JavaScript requests?

I'm using the following code:

Go

type ResponseData struct {
    Message string `json:"message"`
}

w.Header().Set("Access-Control-Allow-Origin", "*")
w.Header().Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE")
w.Header().Set("Access-Control-Allow-Headers", "Accept, Content-Type, Content-Length, Authorization")

json.NewEncoder(w).Encode(ResponseData{Message: "Hello, World"})

JavaScript

fetch('http://localhost:8080/get', {
  method: "GET"
})
.then(res => res.json())
.then(data => console.log(data))
.catch(err => console.log(err.message))

The code is working fine, but when someone enters http://localhost:8080/get, it shows {"message":"Hello, World"}, is there a way to get the object only in JavaScript?