Example snippet code to post the content of a form to a rest api which then returns some json response using kotlin compiled (=transpiled) to javascript and the fetch api

Kotlin_JS_SubmitFormViaFetch.kt

// This is an example snippet code to post the content of a form to a rest api which
// then returns some json response using kotlin compiled (=transpiled) to javascript
// 
// <form method="POST" action="<url to rest api which returns json>">
//  ...fields...
//  <input type="button" id="my-submit-button" value="Click Me!">
// </form>

import org.w3c.dom.HTMLInputElement
import org.w3c.xhr.FormData
import org.w3c.fetch.RequestInit
import kotlin.browser.*

fun submitForm(submitElt: HTMLInputElement, handler: (dynamic) -> Unit) {
  submitElt.form?.let { form ->
    window.fetch(form.action,
                 RequestInit(method = form.method,
                             body = FormData(form)))
        .then { response ->
          if (response.status == 200.toShort()) {
            response.json()
          } else
            println("there was an error...${response.status}")
        }
        .then { json: dynamic ->
          handler(json)
        }
  }
}

fun main(args: Array<String>) {
    val elt = document.getElementById("my-submit-button") as HTMLInputElement
    submitForm(elt) { json -> // here json is "dynamic" => access like in plain js
        println("success from request => ${json.uri}")
    }
}

/*
This is the transpiled result...

kotlin.kotlin.io.output.flush();
if (typeof kotlin === 'undefined') {
  throw new Error("Error loading module 'moduleId'. Its dependency 'kotlin' was not found. Please, check whether 'kotlin' is loaded prior to 'moduleId'.");
}
var moduleId = function (_, Kotlin) {
  'use strict';
  var toShort = Kotlin.toShort;
  var println = Kotlin.kotlin.io.println_s8jyv4$;
  var Unit = Kotlin.kotlin.Unit;
  var throwCCE = Kotlin.throwCCE;
  function submitForm$lambda$lambda(response) {
    if (response.status === toShort(200)) {
      return response.json();
    }
     else
      return println('there was an error...' + response.status), Unit;
  }
  function submitForm$lambda$lambda_0(closure$handler) {
    return function (json) {
      closure$handler(json);
      return Unit;
    };
  }
  function submitForm(submitElt, handler) {
    var tmp$;
    if ((tmp$ = submitElt.form) != null) {
      var tmp$_0 = window;
      var tmp$_1 = tmp$.action;
      var method = tmp$.method;
      var body = new FormData(tmp$);
      var headers;
      var referrer;
      var referrerPolicy;
      var mode;
      var credentials;
      var cache;
      var redirect;
      var integrity;
      var keepalive;
      var window_0;
      headers = undefined;
      referrer = undefined;
      referrerPolicy = undefined;
      mode = undefined;
      credentials = undefined;
      cache = undefined;
      redirect = undefined;
      integrity = undefined;
      keepalive = undefined;
      window_0 = undefined;
      var o = {};
      o['method'] = method;
      o['headers'] = headers;
      o['body'] = body;
      o['referrer'] = referrer;
      o['referrerPolicy'] = referrerPolicy;
      o['mode'] = mode;
      o['credentials'] = credentials;
      o['cache'] = cache;
      o['redirect'] = redirect;
      o['integrity'] = integrity;
      o['keepalive'] = keepalive;
      o['window'] = window_0;
      tmp$_0.fetch(tmp$_1, o).then(submitForm$lambda$lambda).then(submitForm$lambda$lambda_0(handler));
    }
  }
  function main$lambda(json) {
    println('success from request => ' + json.uri.toString());
    return Unit;
  }
  function main(args) {
    var tmp$;
    var elt = Kotlin.isType(tmp$ = document.getElementById('my-submit-button'), HTMLInputElement) ? tmp$ : throwCCE();
    submitForm(elt, main$lambda);
  }
  _.submitForm_9lm2sa$ = submitForm;
  _.main_kand9s$ = main;
  main([]);
  Kotlin.defineModule('moduleId', _);
  return _;
}(typeof moduleId === 'undefined' ? {} : moduleId, kotlin);

kotlin.kotlin.io.output.buffer;
*/