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HTML 

              
                <label for="search">Find a Canadian City</label>
<input id="search" name="search" placeholder="Windsor"/>
<h4>Results</h4>
<pre class="results-area"></pre>
!

CSS 

              
                body, input {
  font-family: sans-serif;
  font-size:1.5em;
}

fieldset {
  padding:0.5em;
  border-width:0;
}

input[type=checkbox] {
  height:1.5em;
  width:1.5em;
}

ul {
  margin:0;
  padding:0;
}

li {
  margin:0;
  list-style-type:none;
}

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

.hidden {
  display:none;
}

@keyframes rotate {
  0%    { transform: rotate(0deg); }
  100%  { transform: rotate(360deg); }
}
!

JS 

              
                const { fromEvent } = rxjs;
const { debounceTime, tap, switchMap, flatMap } = rxjs.operators;

const searchField = document.querySelector("[name=search]");
const resultsArea = document.querySelector(".results-area");

const changes$ = fromEvent(searchField, "input");

changes$
  .pipe(
    // debouncing is a good idea, but makes it harder demonstrate the point of this post
    // debounceTime(400),

    // what would happen if you used flatMap instead of switchMap here? Answer is at then end of the source code
    switchMap(event => fakeSearch(event.target.value))
  )
  .subscribe(result => {
    resultsArea.innerText =
      JSON.stringify(result, null, 2);
  });

/**
 * End of real frontend code.
 * This stuff provides a fake backend - an async function that returns search results
 */

function roughDelay() {
  return new Promise(resolve =>
    setTimeout(resolve, 250 + Math.random() * 3000)
  );
}

function fakeSearch(keyword) {
  return roughDelay().then(() => {
    return fuse.search(keyword);
  });
}

var options = {
  caseSensitive: false,
  shouldSort: true,
  threshold: 0.6,
  location: 0,
  distance: 100,
  maxPatternLength: 32,
  minMatchCharLength: 1,
  keys: ["name"]
};

const list = [
  "Toronto",
  "Montreal",
  "Calgary",
  "Ottawa",
  "Edmonton",
  "Mississauga",
  "Winnipeg",
  "Vancouver",
  "Brampton",
  "Hamilton",
  "Quebec City",
  "Surrey",
  "Laval",
  "Halifax",
  "London",
  "Markham",
  "Vaughan",
  "Gatineau",
  "Saskatoon",
  "Longueuil",
  "Kitchener",
  "Burnaby",
  "Windsor",
  "Regina",
  "Richmond",
  "Richmond Hill",
  "Oakville",
  "Burlington",
  "Greater Sudbury",
  "Sherbrooke",
  "Oshawa",
  "Saguenay",
  "Lévis",
  "Barrie",
  "Abbotsford",
  "Coquitlam",
  "Trois-Rivières",
  "St. Catharines",
  "Guelph",
  "Cambridge",
  "Whitby",
  "Kelowna",
  "Kingston",
  "Ajax",
  "Langley",
  "Saanich",
  "Terrebonne",
  "Milton",
  "St. John's",
  "Thunder Bay",
  "Waterloo",
  "Delta",
  "Chatham-Kent",
  "Red Deer",
  "Strathcona County",
  "Brantford",
  "Saint-Jean-sur-Richelieu",
  "Cape Breton",
  "Lethbridge",
  "Clarington",
  "Pickering",
  "Nanaimo",
  "Kamloops",
  "Niagara Falls",
  "Victoria",
  "Brossard",
  "Repentigny",
  "Newmarket",
  "Chilliwack",
  "Maple Ridge",
  "Peterborough",
  "Kawartha Lakes",
  "Drummondville",
  "Saint-Jérôme",
  "Prince George",
  "Sault Ste. Marie",
  "Moncton",
  "Sarnia",
  "Wood Buffalo",
  "New Westminster",
  "Saint John",
  "Caledon",
  "Granby",
  "St. Albert",
  "Norfolk County",
  "Medicine Hat",
  "Grande Prairie",
  "Airdrie",
  "Halton Hills",
  "Port Coquitlam",
  "Fredericton",
  "Blainville",
  "Saint-Hyacinthe",
  "Aurora",
  "North Vancouver",
  "Welland",
  "North Bay",
  "Belleville",
  "Mirabel"
].map(name => ({ name }));

const fuse = new Fuse(list, options);

// flatMap results in every response from the server being rendered, even outdated responses (since they don't always come back  to the browser in the order they were requested)
// flatMap(event => fakeSearch(event.target.value))

// switchMap ignores results from outdated search requests, which gives us the desired behaviour
// switchMap(event => fakeSearch(event.target.value))
!
999px

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