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HTML Settings

Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

  <legend>Grocery List</legend>
        <input type="checkbox" name="grocery-list" value="sweet-potato" id="sweet-potato">
        <label for="sweet-potato">🍠 Sweet Potato</label>
        <div class="spinner hidden"></div>

        <input type="checkbox" name="grocery-list" value="pineapple" id="pineapple">
        <label for="pineapple">🍍 Pineapple</label>
        <div class="spinner hidden"></div>
        <input type="checkbox" name="grocery-list" value="watermelon" id="watermelon">
        <label for="watermelon">🍉 Watermelon</label>
        <div class="spinner hidden"></div>

<pre class="results-area"></pre>
              body {
  font-family: sans-serif;

fieldset {

input[type=checkbox] {

ul {

li {

.spinner {
  border: 3px solid #444;
  border-right-color: transparent;
  border-radius: 100%;
  margin: 0 10px;
  height: 16px;
  width: 16px;
  animation: rotate 1s infinite linear;

.hidden {

@keyframes rotate {
  0%    { transform: rotate(0deg); }
  100%  { transform: rotate(360deg); }
              const { fromEvent, from } = rxjs;
const { debounceTime, map, tap, switchMap, flatMap } = rxjs.operators;

const fieldset = document.querySelector("fieldset");
const resultsArea = document.querySelector(".results-area");

const eventToRequestBody = event => ({

const changes1$ = fromEvent(fieldset, "input");

    tap(requestBody => setItemInteractivity(, false)),
  // what happens if you use switchMap here? Answer is at the bottom of the pen
    flatMap(requestBody => {
      return from(fakeSave(requestBody)).pipe(
        map(saveResponse => ({ ...requestBody, response: saveResponse }))
   tap(responseInfo => setItemInteractivity(, true)),
  .subscribe(text => (resultsArea.innerText = text));

const setItemInteractivity = (id, active) => {
  const spinner = document.querySelector(`label[for=${id}] + div`)
  active ? spinner.classList.add('hidden') : spinner.classList.remove('hidden')

 * End of real frontend code.
 * This stuff provides a fake backend - an async function that returns results of writing data
function roughDelay() {
  return new Promise(resolve =>
    setTimeout(resolve, 100 + Math.random() * 3000)

function fakeSave(data) {
  return roughDelay().then(() => {
    return Math.random() > 0.7;

// if we use switchMap here, the app only cares about the most recent http request, and activity indicators for previous http requests aren't removed when the response completes if multiple updates are happening at once
// switchMap(requestBody => {

// since flatMap does not discard any events, every http request that finishes stays in the stream
// flatMap(requestBody => {

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