JSFiddle - React, Tailwind, and code Playground

by John Semblante

HTML

<form autocomplete="off" action="/action_page.php">
  <div class="autocomplete" style="width:300px;">
    <input id="myInput" type="text" name="myCountry" placeholder="Country">
  </div>
  <input type="submit">
</form>

CSS

* { box-sizing: border-box; }
body {
  font: 16px Arial; 
}
.autocomplete {
  /*the container must be positioned relative:*/
  position: relative;
  display: inline-block;
}
input {
  border: 1px solid transparent;
  background-color: #f1f1f1;
  padding: 10px;
  font-size: 16px;
}
input[type=text] {
  background-color: #f1f1f1;
  width: 100%;
}
input[type=submit] {
  background-color: DodgerBlue;
  color: #fff;
}
.autocomplete-items {
  position: absolute;
  border: 1px solid #d4d4d4;
  border-bottom: none;
  border-top: none;
  z-index: 99;
  /*position the autocomplete items to be the same width as the container:*/
  top: 100%;
  left: 0;
  right: 0;
}
.autocomplete-items div {
  padding: 10px;
  cursor: pointer;
  background-color: #fff; 
  border-bottom: 1px solid #d4d4d4; 
}
.autocomplete-items div:hover {
  /*when hovering an item:*/
  background-color: #e9e9e9; 
}
.autocomplete-active {
  /*when navigating through the items using the arrow keys:*/
  background-color: DodgerBlue !important; 
  color: #ffffff; 
}

JavaScript

function autocomplete(inp, arr) {
  /*the autocomplete function takes two arguments,
  the text field element and an array of possible autocompleted values:*/
  var currentFocus;
  /*execute a function when someone writes in the text field:*/
  inp.addEventListener("input", function(e) {
      var a, b, i, val = this.value;
      /*close any already open lists of autocompleted values*/
      closeAllLists();
      if (!val) { return false;}
      currentFocus = -1;
      /*create a DIV element that will contain the items (values):*/
      a = document.createElement("DIV");
      a.setAttribute("id", this.id + "autocomplete-list");
      a.setAttribute("class", "autocomplete-items");
      /*append the DIV element as a child of the autocomplete container:*/
      this.parentNode.appendChild(a);
      /*for each item in the array...*/
      for (i = 0; i < arr.length; i++) {
        /*check if the item starts with the same letters as the text field value:*/
        if (matchWord(val.toUpperCase(),arr[i].toUpperCase()) !== -1 ) {
        	var matchLength = matchWord(val.toUpperCase(),arr[i].toUpperCase());
          /*create a DIV element for each matching element:*/
          b = document.createElement("DIV");
          /*make the matching letters bold:*/
          b.innerHTML = arr[i].substr(0, val.length);
          
          b.innerHTML += arr[i].substr(val.length);
          b.innerHTML = b.innerHTML.replace(val, "<strong>"+val+"</strong>");
          /*insert a input field that will hold the current array item's value:*/
          b.innerHTML += "<input type='hidden' value='" + arr[i] + "'>";
          /*execute a function when someone clicks on the item value (DIV element):*/
          b.addEventListener("click", function(e) {
              /*insert the value for the autocomplete text field:*/
              inp.value = this.getElementsByTagName("input")[0].value;
              /*close the list of autocompleted values,
              (or any other open lists...