Get Struct /Variables out of Go-Variable per JavaScript/JSON/Ajax

Question

i'm currently trying to send variables (in this case a struct array into the JS variable Data) to my website. In Addition i want to read a String out of my TextField and trigger a Function with it as parameter. My question is, how to get/recieve/send the variable from Go/Javascript? For now it doesnt even call the fillChoiceBox() function. I set it as onClick Function but nothing happens. A Code Example would be very nice.

Here my Golang code:

//Klimakammer struct
type klimakammer struct {
    Name        string `json:"name"`
    Hersteller  string `json:"hersteller"`
    IP          string `json:"ip"`
    SollTemp    string `json:"solltemp"`
    IstTemp     string `json:"isttemp"`
    SollFcht    string `json:"sollfcht"`
    IstFcht     string `json:"istfcht"`
    kammerstart bool
    kammerstop  bool
}

//Ct01 Klimakammern erstellen
var Ct01 = klimakammer{"ct01", "weiss", "10.0.62.22", "", "", "", "", false, true}

//Kammern - Fill Klimakammer Array
var Kammern = []klimakammer{
    Ct01,
}

func main() {

    fs := http.FileServer(http.Dir("./static/"))
    http.Handle("/", fs)

    http.ListenAndServe(":8080", nil)

    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        buff, _ := json.Marshal(&Kammern)
        fmt.Fprintln(w, string(buff))
    })

}

and my JS-Code:

function fillChoiceBox() {

   **//That was my first try (But it never found the URL "/getKammer"):**
 // $.ajax({
 //     url: "http://localhost:8080/getKammer",
 //     method: "GET",
 //     function(data) {
 //         var $dropdown = $("#Kammer");
 //         for( i=0; i <= data.length; i++) {
 //               $dropdown.append($("<option />").val(data[i]).text(this.name));
 //               $("#getKammer").prop('disabled', true);
 //         }
 //     },
 //  })
            var i;
            var $dropdown = $("#Kammer");
            for( i=0; i <= data.length; i++) {
            $dropdown.append($("<option />").val(data[i]));
            }
            $("#getKammer").prop('disabled', true);
  }

Calling HandleFunc/Handle more than once with the same pattern will panic (currently your code doesn't panic because the second call is not reached thanks to ListenAndServe). — mkopriva
– mkopriva, Commented Jun 10, 2020 at 6:13
and as i said my previous try was with /getKammer but the developerConsole of Chrome said that /getKammer is not there — SleepWalk3r
– SleepWalk3r, Commented Jun 10, 2020 at 6:20
Use a separate endpoint, using "/" is not a requirement, you can substitute it with whatever else (within reason). — mkopriva
– mkopriva, Commented Jun 10, 2020 at 6:21

poWar · Accepted Answer · 2020-06-10 06:25:12Z

1

Here is a sample code to send and get data from a typical Go Server. Before implementing, I would suggest going through this blog about writing web applications with Go.

package main

import (
    "encoding/json"
    "log"
    "net/http"
)

type Foo struct {
    Field1 string `json:"field1"`
    Field2 int    `json:"field2"`
}

func main() {
    http.HandleFunc("/foo", func(w http.ResponseWriter, r *http.Request) {
        var f Foo
        if err := json.NewDecoder(r.Body).Decode(&f); err != nil {
            panic(err)
        }
        defer r.Body.Close()

        log.Println("foo: ", f)
        w.WriteHeader(http.StatusOK)
    })

    http.HandleFunc("/bar", func(w http.ResponseWriter, _ *http.Request) {
        f := Foo{"bar", 20}
        w.Header().Set("Content-Type", "application/json")
        if err := json.NewEncoder(w).Encode(&f); err != nil {
            panic(err)
        }
    })

    panic(http.ListenAndServe(":3030", nil))
}

/*
JS Code to post data:

$.ajax({
    url: "http://localhost:3030/foo",
    method: "POST",
    data: JSON.stringify({field1:"foo",field2:10}),
    success: function() {
        console.log('done');
    }
})

JS Code to get data:

$.ajax({
    url: "http://localhost:3030/bar",
    method: "GET",
    success: function(data) {
        console.log(data);
    }
})
*/

edited Jun 10, 2020 at 6:25

answered Jun 10, 2020 at 6:20

poWar

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1 Comment

poWar Over a year ago

Like @mkopriva mentioned in the comments, its still important for you to understand the basics of a go web server. ListenAndServe is a blocking call. This means, your program will not proceed beyond that. So in your original question http.HandleFunc("/" is unreachable code. Please read through the blog I linked to get a better understanding.

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