How To Implement JQuery AutoComplete

JQuery Autocomplete enhances the UI functionality of visualforce page, when a user types in a field it quickly find and select from a pre-populated list of values, leveraging searching and filtering. We can achieve this functionality by using Jquery with Ajax or by using custom controller in Salesforce.

Here is example in which i am using both option's, Account is coming from the controller and the contact records that we are getting is by using Ajax.

Code for Controller:

public class AutoCompleteJQueryController{
    //list which returns accounts records
    public list getAccountRecords(){
        return [select id,name from account limit 25];
    }
}

<!-- Javascript/JQuery Links-->
<script src="https://code.jquery.com/jquery-1.8.2.js"></script>
<script src="/soap/ajax/26.0/connection.js" type="text/javascript"></script>
<script src="https://code.jquery.com/ui/1.9.0/jquery-ui.js"></script>

<apex:page controller="AutoCompleteJQueryController">
    <!-- Javascript/JQuery Links-->
    <script src="https://code.jquery.com/jquery-1.8.2.js"></script>
    <script src="/soap/ajax/26.0/connection.js" type="text/javascript"></script>
    <script src="https://code.jquery.com/ui/1.9.0/jquery-ui.js"></script>
    <link rel="stylesheet" href="https://code.jquery.com/ui/1.9.1/themes/base/jquery-ui.css"/>
    <script type="text/javascript">
        var j$ = jQuery.noConflict();
        var autoAccountList =[];         
        //use the <!-- <apex:repeat > --> tag to assign controller List values to javascript variable.
        <apex:repeat value="{!AccountRecords}" var="accList">
            //Store the name of the account in the array variable.
            autoAccountList.push('{!accList.name}');
        </apex:repeat>         
        // Establish a connection with salesforce database using the sforce.connection.init(sessionID, ServerURL) function.
        var sessionId = '{!$Api.Session_ID}';
        var server = "https://" + window.location.host + "/services/Soap/u/26.0";
        sforce.connection.init(sessionId, server);         
        //Here we query the contact object using the sforce.connection.query function. This will return 200 results.
        var result = sforce.connection.query("select Name from Contact");
        var records = result.getArray("records");
        var ContactList =[];         
        //Traverse the list of contact and store the value in javascript array variable which will then assign those values to the source of the autocomplete.
        for(i=0;i<records.length;i++){
            ContactList[i]=records[i].Name;
        }
        //on Document ready
        j$(document).ready(function(){             
            j$("#accountAutocomplete").autocomplete({
                source : autoAccountList
            });
            j$("#ajaxContactAutocomplete").autocomplete({
                source : ContactList
            });
        });      
    </script>     
    <apex:form >
        <b>Account(This list is coming from the Apex class)</b><input type="text" id="accountAutocomplete"/><br/><br/>
        <b>Contact(This list is coming from salesforce's ajax toolkit)</b><input type="text" id="ajaxContactAutocomplete"/>
    </apex:form>     
</apex:page>