JavaScript POST request to Golang server error – Unexpected end of JSON input

Issue

I am making a POST request in JavaScript to my Go server to POST some JSON data. The backend recieves the data succesfully.
If I console log the result of the promise I get Unexpected end of JSON input error at line where fetchResponse.json() is called. I cant figure out why it is happening.

JavaScript

const sendScore = async () => {

    try {
        const fetchResponse = await fetch(`http://localhost:8000/sendscore`, {
            method: 'POST',
            headers: {
                'Accept': 'application/json',
                'Content-Type': 'application/json'
            },

            body: JSON.stringify({name:"kris"})
        });

        const data = await fetchResponse.json();
        return data;

    } catch (e) {
        return e;
    }
}

const sendScoreBtn = document.querySelector("#sendScoreBtn");
sendScoreBtn.addEventListener("click", () => {
    console.log("Sending score...")
    const res = sendScore()
    res.then(console.log)

})

Go /sendscore endpoint handler

func recieveScore(w http.ResponseWriter, r *http.Request) {
    var res playerScore
    if err := json.NewDecoder(r.Body).Decode(&res); err != nil {
        fmt.Println("Line 31", err)
    }

    fmt.Println("Res", res)
}

func main() {

    // Serve static files(js, css)
    http.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.Dir("./static"))))
    http.HandleFunc("/", homePage)
    http.HandleFunc("/sendscore", recieveScore)

    fmt.Println("Server started. Listening on port :8000")
    log.Fatal(http.ListenAndServe(":8000", nil))
}

Solution

My problem was not sending response back to the browser and therefore it couldnt parse any JSON.
Updated Go handler, which made the process work.

func recieveScore(w http.ResponseWriter, r *http.Request) {
    var res playerScore
    if err := json.NewDecoder(r.Body).Decode(&res); err != nil {
        fmt.Println("Line 31", err)
    }

    fmt.Println("Res", res)
    
    w.Header().Set("Content-Type", "application/json")
    json.NewEncoder(w).Encode(res) // Writing the result to response
}

Answered By – Kristofer Kangro

Answer Checked By – Candace Johnson (GoLangFix Volunteer)

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