javascript - Autocomplete with Search as you type anywhere matching and validation

function fruitautocomplete(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 (arr[i].substr(0, val.length).toUpperCase() == val.toUpperCase()) {
        /*create a DIV element for each matching element:*/
        b = document.createElement("DIV");
        /*make the matching letters bold:*/
        b.innerHTML = "<strong>" + arr[i].substr(0, val.length) + "</strong>";
        b.innerHTML += arr[i].substr(val.length);
        /*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 of autocompleted values:*/
          closeAllLists();
        });
        a.appendChild(b);
      }
    }
  });
  /*execute a function presses a key on the keyboard:*/
  inp.addEventListener("keydown", function(e) {
    var x = document.getElementById(this.id + "autocomplete-list");
    if (x) x = x.getElementsByTagName("div");
    if (e.keyCode == 40) {
      /*If the arrow DOWN key is pressed,
      increase the currentFocus variable:*/
      currentFocus++;
      /*and and make the current item more visible:*/
      addActive(x);
    } else if (e.keyCode == 38) { //up
      /*If the arrow UP key is pressed,
      decrease the currentFocus variable:*/
      currentFocus--;
      /*and and make the current item more visible:*/
      addActive(x);
    } else if (e.keyCode == 13) {
      /*If the ENTER key is pressed, prevent the form from being submitted,*/
      e.preventDefault();
      if (currentFocus > -1) {
        /*and simulate a click on the "active" item:*/
        if (x) x[currentFocus].click();
      }
    }
  });

  function addActive(x) {
    /*a function to classify an item as "active":*/
    if (!x) return false;
    /*start by removing the "active" class on all items:*/
    removeActive(x);
    if (currentFocus >= x.length) currentFocus = 0;
    if (currentFocus < 0) currentFocus = (x.length - 1);
    /*add class "autocomplete-active":*/
    x[currentFocus].classList.add("autocomplete-active");
  }

  function removeActive(x) {
    /*a function to remove the "active" class from all autocomplete items:*/
    for (var i = 0; i < x.length; i++) {
      x[i].classList.remove("autocomplete-active");
    }
  }

  function closeAllLists(elmnt) {
    /*close all autocomplete lists in the document,
    except the one passed as an argument:*/
    var x = document.getElementsByClassName("autocomplete-items");
    for (var i = 0; i < x.length; i++) {
      if (elmnt != x[i] && elmnt != inp) {
        x[i].parentNode.removeChild(x[i]);
      }
    }
  }
  /*execute a function when someone clicks in the document:*/
  document.addEventListener("click", function(e) {
    closeAllLists(e.target);
  });
}

/*An array containing all the country names in the world:*/
var fruitlist = [
  "Apple",
  "Mango",
  "Pear",
  "Banana",
  "Berry"
];

/*initiate the autocomplete function on the "myFruitList" element, and pass along the fruit array as possible autocomplete values:*/
autocomplete(document.getElementById("myFruitList"), fruitlist);

* {
  box-sizing: border-box;
}

body {
  background-color: #f1f1f1;
}

#regForm {
  background-color: #ffffff;
  margin: 10px auto;
  font-family: Raleway;
  padding: 10px;
  width: 90%;
  min-width: 300px;
}

h1 {
  text-align: center;
}

input {
  padding: 10px;
  width: 100%;
  font-size: 17px;
  font-family: Raleway;
  border: 1px solid #aaaaaa;
}


/* Mark input boxes that gets an error on validation: */

input.invalid {
  background-color: #ffdddd;
}


/* Hide all steps by default: */

.tab {
  display: none;
}

button {
  background-color: #04AA6D;
  color: #ffffff;
  border: none;
  padding: 10px 20px;
  font-size: 17px;
  font-family: Raleway;
  cursor: pointer;
}

button:hover {
  opacity: 0.8;
}

#prevBtn {
  background-color: #bbbbbb;
}


/* Make circles that indicate the steps of the form: */

.step {
  height: 15px;
  width: 15px;
  margin: 0 2px;
  background-color: #bbbbbb;
  border: none;
  border-radius: 50%;
  display: inline-block;
  opacity: 0.5;
}

.step.active {
  opacity: 1;
}


/* Mark the steps that are finished and valid: */

.step.finish {
  background-color: #04AA6D;
}

<form id="regForm" action="/submit_page.php">
  <h1>Your Nutrition Needs:</h1>
  <div class="tab">Your Fruit:
    <p class="autocomplete">
      <input id="myFruitList" type="text" name="fruit" placeholder="Start typing your fruit name"></p>
  </div>
</form>

Solution:

I think you are looking for functionality which is on the "Symbol" field of the form on this page: https://zerodha.com/margin-calculator/SPAN/

It has the standard drop-down, when cursor place it shows all possible entries (1) plus a search box, it does anywhere string search match (2), and may be (3) is also available. Check its source code to see if that helps.

Thank you

Solution:

I managed to find a simple answer, and its a moral obligation on my part to post it for everyone's benefit :-)

<link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/css/select2.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/select2.full.min.js"></script>


<hr>
<select class="js-example-basic-single" name="state">
  <option value="AL">Alabama</option>
  <option value="NY">New York</option>
  <option value="WY">Wyoming</option>
</select>
<script>
$(document).ready(function() {
    $('.js-example-basic-single').select2();
});
</script>

For more details, check https://select2.org/ documentation