Autocomplete with Large Dataset - ASP.Net

 Friends, You might have used jquery autocomplete to a search field in your website. But have you ever wondered to deal with large datasets? JQuery auto complete makes the page unresponsive with it's search if there are lot of data to filter. Below is the solution to that. 

Original post for this can be found here

     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 (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);  
       });  
     }  

And you will have to apply the following CSS.

 /*the container must be positioned relative:*/  
 .autocomplete {  
   position: relative;  
   display: inline-block;  
 }  
 .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;  
   max-height: 300px;  
   /*height: 300px;*/  
   overflow-y: auto;  
   margin-left: 20px;  
 }  
   .autocomplete-items div {  
     padding: 5px 15px;  
     cursor: pointer;  
     background-color: #fff;  
     border-bottom: 1px solid #d4d4d4;  
   }  
     /*when hovering an item:*/  
     .autocomplete-items div:hover {  
       background-color: #e9e9e9;  
     }  
 /*when navigating through the items using the arrow keys:*/  
 .autocomplete-active {  
   background-color: DodgerBlue !important;  
   color: #ffffff;  
 }  

Then the reference can be made as below;

 autocomplete(document.getElementById("txtSearch"), keywords);  

Keywords are the array of strings to search. So, it will look like below eventually,

Unlike jquery autocomplete, this doesn't slowdown your page. 

Happy coding..