Javascript in Web-to-Case form

Question

I want to include javascript in my web-to-case from. My sole purpose of doing so is to Query from Salesforce Database in that form. How can I achieve this functionality. Can I use some controller as extension to my Web-to-Case form?

--> alert('dgdgg'); var chatt = sforce.connection.query("SELECT Id FROM LiveChatButton where DeveloperName = 'Chat_Button'") ;

        var deploy = sforce.connection.query("SELECT Id FROM LiveChatDeployment where DeveloperName = 'Customer_Support_Chat'") ;  
    </script>
    <form name="myformMSG" id="myformMSG" hidden="true">
        <label id="prova"></label>
    </form>

    <form id="myform" name="myform" action="https://www.salesforce.com/servlet/servlet.WebToCase?encoding=UTF-8"  method="POST">
    <input type="hidden" name="orgid" value="{!$Organization.Id}"/>
    <input type="hidden" name="retURL" value="{!$Site.Domain}{!URLFOR($Page.Thanks)}"/>

Answer 1

<apex:page standardcontroller="case" extensions="CaseExt">
    <script>
        var chatt = sforce.connection.query("SELECT Id FROM LiveChatButton where DeveloperName = 'Chat_Button'") ;
        var deploy = sforce.connection.query("SELECT Id FROM LiveChatDeployment where DeveloperName = 'Customer_Support_Chat'") ;  
    </script>
    <form name="myformMSG" id="myformMSG" hidden="true">
        <label id="prova"></label>
    </form>

    <form id="myform" name="myform" action="https://www.salesforce.com/servlet/servlet.WebToCase?encoding=UTF-8"  method="POST">
    <input type="hidden" name="orgid" value="{!$Organization.Id}"/>
    <input type="hidden" name="retURL" value="{!$Site.Domain}{!URLFOR($Page.Thanks)}"/>

    User Name : <input type="text" value="{!user.Username}" />
</apex:page>

Controller

public class CaseExt {
    public user user;
    public CaseExt (ApexPages.StandardController stdController) {
        user = [SELECt Id, Username from user where Id =: userIfo.getuserId()];
    }
}

This is a just simple piece of code to give you understanding how you can use extension in your form