Golang - multiple response values in web app

Question

I write simple go web app. In this app, i am sending ajax post request and returning simple "hello world!" string and print it in console, but something is strange. There is three response value in console output. One with empty value and two response with "hello world!" string values. What is wrong with my code?

Golang Code:

package main

import (
    "io"
    "net/http"
    "html/template"
)

func main() {
     http.HandleFunc("/ajax", ajaxHandler)
     http.HandleFunc("/script.js", srcHandler)
     http.HandleFunc("/", mainHandler)
     http.ListenAndServe(":8080", nil)
}

func mainHandler(w http.ResponseWriter, r *http.Request) {
    t, err := template.ParseFiles("home.html")
    if err != nil {
        http.Error(w, http.StatusText(500), 500)
        return
    }

    err = t.Execute(w, nil)
    if err != nil {
        http.Error(w, http.StatusText(500), 500)
        return
    }
}

func srcHandler(w http.ResponseWriter, r *http.Request) {
     http.ServeFile(w, r, "script.js")
}

func ajaxHandler(w http.ResponseWriter, r *http.Request) {
    io.WriteString(w, "Hello World!")
}

Javascript Code:

(function () {
    window.onclick = function () {
        var req = new XMLHttpRequest();
        req.open("post", "/ajax", true);
        req.send();

        req.onreadystatechange = function () {
            console.log(req.responseText);
       }
   };
}());

The Go code looks OK, so your issue is likely in the client-side code, which wasn't listed. — Adrian
– Adrian, Commented Apr 25, 2017 at 20:49
Are you sure the first output string is from that very endpoint? Show the network tab screenshot and your corresponding js code. — zerkms
– zerkms, Commented Apr 25, 2017 at 20:54

zerkms · Accepted Answer · 2017-04-25 21:01:23Z

3

You need to additionally check the req.readyState:

   req.onreadystatechange = function () {
        if (req.readyState === XMLHttpRequest.DONE) {
            console.log(req.responseText);
        }
   }

References:

https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/onreadystatechange

answered Apr 25, 2017 at 21:01

zerkms

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